JavaScript 中的
WeakMap 是一个键值对的集合，其中键必须是 objects，以及对这些对象的引用键很“弱”。这意味着如果没有其他对关键对象的引用，即使它仍在 WeakMap 中，它也可以被垃圾回收。
键必须是对象:
弱引用：
不可迭代:
对于私人数据有用：
const weakMap = new WeakMap();
| Method | Description |
|---|---|
| weakMap.set(key, value) | Adds a new key-value pair or updates an existing key. |
| weakMap.get(key) | Retrieves the value associated with the key. |
| weakMap.has(key) | Checks if the key exists in the WeakMap. |
| weakMap.delete(key) | Removes the key-value pair associated with the key. |
const weakMap = new WeakMap();
const weakMap = new WeakMap();
const obj1 = { name: "Alice" };
const obj2 = { name: "Bob" };
// Adding key-value pairs
weakMap.set(obj1, "Data for Alice");
weakMap.set(obj2, "Data for Bob");
// Accessing values
console.log(weakMap.get(obj1)); // Output: "Data for Alice"
// Checking existence
console.log(weakMap.has(obj2)); // Output: true
// Removing a key-value pair
weakMap.delete(obj2);
console.log(weakMap.has(obj2)); // Output: false
let obj = { key: "value" };
const weakMap = new WeakMap();
weakMap.set(obj, "Some data");
// Remove all references to `obj`
obj = null;
// The `WeakMap` entry for `obj` is automatically removed by garbage collection.
const privateData = new WeakMap();
class User {
constructor(name) {
privateData.set(this, { name });
}
getName() {
return privateData.get(this).name;
}
}
const user = new User("Alice");
console.log(user.getName()); // Output: "Alice"
综上所述，WeakMap 是一个专门为需要弱引用和私有关联的场景而设计的集合。
JavaScript 中 Map 和 WeakMap 之间的主要区别在于它们对键、垃圾收集和功能的处理。详细对比如下：
| Feature | Map | WeakMap |
|---|---|---|
| Key Types | Keys can be any type: objects, primitives. | Keys must be objects. |
| Garbage Collection | Does not rely on garbage collection; keys persist. | Keys are held weakly and can be garbage-collected. |
| Iteration | Iterable (can use for...of, forEach, etc.). | Not iterable (cannot list keys or values). |
| Size Property | Has a size property to get the number of entries. | No size property available. |
| Use Case | General-purpose key-value storage. | Specialized for associating metadata or private data with objects. |
| Performance | Slightly slower due to strong key references. | Faster for memory-sensitive operations due to weak references. |
const weakMap = new WeakMap();
const weakMap = new WeakMap();
const obj1 = { name: "Alice" };
const obj2 = { name: "Bob" };
// Adding key-value pairs
weakMap.set(obj1, "Data for Alice");
weakMap.set(obj2, "Data for Bob");
// Accessing values
console.log(weakMap.get(obj1)); // Output: "Data for Alice"
// Checking existence
console.log(weakMap.has(obj2)); // Output: true
// Removing a key-value pair
weakMap.delete(obj2);
console.log(weakMap.has(obj2)); // Output: false
let obj = { key: "value" };
const weakMap = new WeakMap();
weakMap.set(obj, "Some data");
// Remove all references to `obj`
obj = null;
// The `WeakMap` entry for `obj` is automatically removed by garbage collection.
const privateData = new WeakMap();
class User {
constructor(name) {
privateData.set(this, { name });
}
getName() {
return privateData.get(this).name;
}
}
const user = new User("Alice");
console.log(user.getName()); // Output: "Alice"
示例：
const metadata = new WeakMap();
function trackElement(element) {
metadata.set(element, { clicks: 0 });
}
function incrementClicks(element) {
const data = metadata.get(element);
if (data) {
data.clicks++;
}
}
const button = document.createElement("button");
trackElement(button);
incrementClicks(button);
console.log(metadata.get(button)); // Output: { clicks: 1 }
示例：
const map = new Map();
map.set(1, "value"); // Allowed
map.set("key", "value"); // Allowed
map.set({}, "value"); // Allowed
const weakMap = new WeakMap();
weakMap.set({}, "value"); // Allowed
weakMap.set(1, "value"); // TypeError: Invalid value used as weak map key
| Feature | Map | WeakMap |
|---|---|---|
| Flexibility | General-purpose, flexible. | Specialized, limited use case. |
| Performance | Persistent key references. | Memory-efficient with weak references. |
| Suitability | Iteration and long-term storage. | Private data and ephemeral relationships. |
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