Thêm khóa/giá trị vào đối tượng mảng JavaScript

Bản đồ là tập hợp các mục dữ liệu có khóa, giống như một

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Các phương thức và thuộc tính là

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  7 – tạo bản đồ

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  8 – lưu trữ giá trị bằng khóa

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  9 – trả về giá trị theo khóa,

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  0 nếu

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  1 không tồn tại trên bản đồ

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  2 – trả về

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  3 nếu tồn tại

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  1, ngược lại là

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  5

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  6 – xóa phần tử (cặp khóa/giá trị) bằng khóa

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  7 – xóa mọi thứ khỏi bản đồ

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  8 – trả về số lượng phần tử hiện tại

Ví dụ

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Như chúng ta có thể thấy, không giống như các đối tượng, các khóa không được chuyển thành chuỗi. Bất kỳ loại chìa khóa là có thể

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Mặc dù

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Vì vậy, chúng ta nên sử dụng phương pháp

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Bản đồ cũng có thể sử dụng các đối tượng làm chìa khóa

Ví dụ

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Sử dụng các đối tượng làm chìa khóa là một trong những tính năng quan trọng và đáng chú ý nhất của

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Hãy thử

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

Vì

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Cách

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Để kiểm tra sự tương đương của các khóa,

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Thuật toán này không thể thay đổi hoặc tùy chỉnh

xiềng xích

Mỗi cuộc gọi

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Để lặp qua một

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  85 – trả về một lần lặp cho các khóa,

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  86 – trả về một giá trị có thể lặp lại,

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  87 – trả về một lần lặp cho các mục nhập

  let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  88, nó được sử dụng theo mặc định trong

  let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  89

Ví dụ

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Thứ tự chèn được sử dụng

Việc lặp đi lặp lại theo thứ tự như các giá trị đã được chèn vào.

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Bên cạnh đó,

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Khi một

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

Nếu chúng ta có một đối tượng đơn giản và chúng ta muốn tạo một

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Vì vậy, chúng ta có thể tạo bản đồ từ một đối tượng như thế này

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

Ở đây,

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Chúng ta vừa xem cách tạo

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

Có phương thức

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

Chúng ta có thể sử dụng

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

E. g. chúng tôi lưu trữ dữ liệu trong một

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

chúng ta đi đây

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

Một cuộc gọi đến

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

Chúng tôi cũng có thể làm cho dòng

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Điều đó cũng tương tự, bởi vì

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Một

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

phương pháp chính của nó là

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  75 – tạo tập hợp và nếu một đối tượng

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  76 được cung cấp (thường là một mảng), hãy sao chép các giá trị từ đối tượng đó vào tập hợp

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  77 – thêm một giá trị, trả về chính tập hợp đó

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  78 – loại bỏ giá trị, trả về

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  3 nếu

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  10 tồn tại tại thời điểm gọi, nếu không thì

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  5

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  12 – trả về

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  3 nếu giá trị tồn tại trong tập hợp, nếu không thì

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  5

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  15 – loại bỏ mọi thứ khỏi bộ

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  16 – là số nguyên tố

Tính năng chính là các cuộc gọi lặp đi lặp lại của

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Ví dụ: chúng tôi có khách đến và chúng tôi muốn ghi nhớ tất cả mọi người. Nhưng các lượt truy cập lặp đi lặp lại sẽ không dẫn đến trùng lặp. Một khách truy cập phải được "đếm" một lần duy nhất

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Giải pháp thay thế cho

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Chúng ta có thể lặp qua một tập hợp bằng

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Lưu ý điều buồn cười. Hàm gọi lại được truyền trong

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Đó là khả năng tương thích với

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };
let ben = { name: "Ben" };

let visitsCountObj = {}; // try to use an object

visitsCountObj[ben] = 234; // try to use ben object as the key
visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced

// That's what got written!
alert( visitsCountObj["[object Object]"] ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Các phương pháp tương tự mà

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  12 – trả về một đối tượng có thể lặp lại cho các giá trị,

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  13 – giống như

  let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  12, để tương thích với

  let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  3,

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  16 – trả về một đối tượng có thể lặp lại cho các mục nhập

  let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  17, tồn tại để tương thích với

  let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  3

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Phương thức và thuộc tính

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  20 – tạo bản đồ, với tùy chọn

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  76 (e. g. mảng) của

  let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  22 cặp để khởi tạo

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  8 – lưu trữ giá trị theo khóa, trả về chính bản đồ

• let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  9 – trả về giá trị theo khóa,

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  0 nếu

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  1 không tồn tại trên bản đồ

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  2 – trả về

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  3 nếu tồn tại

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  1, ngược lại là

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  5

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  6 – loại bỏ phần tử bằng phím, trả về

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  3 nếu

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  1 tồn tại tại thời điểm gọi, nếu không thì

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  5

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  7 – xóa mọi thứ khỏi bản đồ

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  8 – trả về số lượng phần tử hiện tại

Sự khác biệt so với một

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

• Bất kỳ chìa khóa, đồ vật nào cũng có thể là chìa khóa
• Các phương pháp thuận tiện bổ sung, thuộc tính

  let john = { name: "John" };
  
  // for every user, let's store their visits count
  let visitsCountMap = new Map();
  
  // john is the key for the map
  visitsCountMap.set(john, 123);
  
  alert( visitsCountMap.get(john) ); // 123

  38

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

Phương thức và thuộc tính

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  75 – tạo tập hợp, với tùy chọn

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  76 (e. g. mảng) của các giá trị để khởi tạo

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  77 – thêm một giá trị (không làm gì nếu

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  10 tồn tại), trả về chính tập hợp đó

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  78 – loại bỏ giá trị, trả về

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  3 nếu

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  10 tồn tại tại thời điểm gọi, nếu không thì

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  5

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  12 – trả về

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  3 nếu giá trị tồn tại trong tập hợp, nếu không thì

  let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  5

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  15 – loại bỏ mọi thứ khỏi bộ

• let john = { name: "John" };
  let ben = { name: "Ben" };
  
  let visitsCountObj = {}; // try to use an object
  
  visitsCountObj[ben] = 234; // try to use ben object as the key
  visitsCountObj[john] = 123; // try to use john object as the key, ben object will get replaced
  
  // That's what got written!
  alert( visitsCountObj["[object Object]"] ); // 123

  16 – là số nguyên tố

Việc lặp lại trên

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

let john = { name: "John" };

// for every user, let's store their visits count
let visitsCountMap = new Map();

// john is the key for the map
visitsCountMap.set(john, 123);

alert( visitsCountMap.get(john) ); // 123

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