JavaScript Map和WeakMap有什么区别

在这篇文章中，我们将讨论ES6引入的Map和WeakMap之间的区别。JavaScript对象只支持一个键对象，为了支持多个键对象，Map就应运而生。

Map: Map是一个无序的键值对列表，其中键和值可以是任何类型，如字符串、布尔值、数字等。为了更好地理解，我们来看一个Map和它的属性的示例。

示例: 这个示例展示了在JavaScript中实现Map。

Javascript

// Creating an empty map
const myMap = new Map();
 
// Creating a set by inserting the key-value pair
console.log(myMap);
 
myMap.set("info", { name: "Sam", age: 36 });
 
// Access the elements of a Map
console.log(myMap);
 
console.log(myMap.get("info"));
 
// Checking the element in a Map using has() method
console.log("check whether info is there or not - "
    + myMap.has("info"));
 
// Returning the number of elements using size property
console.log("The no.of elements in a Map are " + myMap.size);
 
// Removing the element from the map using
// clear() and delete() methods
// removing a particular element
myMap.delete("address");
 
myMap.delete("info"); // true
console.log(myMap);
 
// Iteration through the map
// using forEach method()
const map2 = new Map();
map2.set("name", "Sam");
map2.set("age", "36");
 
// looping through Map
map2.forEach(function (value, key) {
    console.log(key + "- " + value);
});

输出

Map(0) {}
Map(1) { 'info' => { name: 'Sam', age: 36 } }
{ name: 'Sam', age: 36 }
check whether info is there or not - true
The no.of elements in a Map are 1
Map(0) {}
name- Sam
age- 36

WeakMap : 在 WeakMap 中，每个键值只能是对象或函数。它用于存储弱对象引用。为了更好的理解，我们来看一个 WeakMap 的示例和它的属性：

示例： 这个示例展示了在 Javascript 中实现 Map 的方式。

Javascript

// Creating a WeakMap
const myweakMap = new WeakMap();
console.log(myweakMap); // WeakMap {} 
 
let obj = {};
 
// Adding object (element) to WeakMap
myweakMap.set(obj, 'hello everyone');
 
console.log(myweakMap);
 
// Access the element of a WeakMap using get() method
console.log("The element of a WeakMap - " + myweakMap.get(obj));
 
// Checking the element in a map using has() method
console.log("check if an element is present in WeakMap - "
    + myweakMap.has(obj));
 
// Delete the element of WeakMap using delete() method
console.log("deleting the element of WeakMap - "
    + myweakMap.delete(obj));
console.log(myweakMap); // WeakMap {}
 
// WeakMaps are not iterable. It will return
// an error. For example,
const weakMap1 = new WeakMap();
console.log(weakMap1); // WeakMap {} 
let obj1 = {};
 
// Adding object (element) to WeakMap
weakMap.set(obj1, 'hello');
 
// Looping through WeakMap
for (let i of weakMap1) {
 
    console.log(i);  // TypeError
}

输出：

WeakMap { <items unknown> }
WeakMap { <items unknown> }
The element of a WeakMap - hello everyone
check if an element is present in WeakMap - true
deleting the element of WeakMap - true
WeakMap { <items unknown> }
WeakMap { <items unknown> }

ReferenceError: weakMap is not defined

Map和WeakMap之间的区别：