The new structures are: 1. Symbol, which represents a unique value and is a function structure; 2. Set, which refers to a "set" structure, similar to an array, allowing the storage of unordered and non-repeated data; 3. WeakSet, similar to Set, the internal data cannot have duplicate values; 4. Map, refers to the "dictionary" structure, which can store mapping relationships.
The operating environment of this tutorial: Windows 7 system, ECMAScript version 6, Dell G3 computer.
ES6 new data structure
1, Symbol
Symbol
isES6 One of the new basic data types in
is a function. Each Symbol
value returned from the Symbol
function is unique, and the symbol
value serves as the identifier of the object attribute and has its only purpose.
const s1 = Symbol() const s2 = Symbol() console.log(s1 === s2); // false
symbol as key
The first way is to add it directly to the literal of the object.
// symbol作为key const obj = { [s1]:'abc', [s2]:'cc', }
The second way is to add it by adding an array.
// 需要用数组方式来获取,不能通过点语法,否则会获取到字符串key console.log(obj[s1]);
The third way is to add it through the defineProperty
method in the object.
const s4=Symbol() Object.defineProperty(obj,s4,{ configurable:true, enumerable:true, writable:true, value:'ff' })
Get the corresponding value through symbol
It needs to be obtained in array mode, not through dot syntax, otherwise the string key will be obtained.
console.log(obj[s1]);
symbol
cannot be implicitly converted to type string
.
Note: The parameter in the Symbol function is the symbol descriptor, which is a new feature in ES10
let Sym = Symbol("Sym") alert(Sym) // TypeError: Cannot convert a Symbol value to a string
We cannot alert
one directly symbol
object, but we can get the descriptor of the symbol
object through toString
or .description
.
let sym = Symbol('a') console.log(sym.description); // 'a'
Traversing symbol
cannot obtain symbol when using
for traversal and
object.keys
Healthy, object
also provides the getOwnPropertySymbols
method, which is used to obtain the keys of all symbols in the object.
const sKeys=(Object.getOwnPropertySymbols(obj)); for(const skey of sKeys){ console.log(obj[skey]); }
Global symbol object registration
Sometimes, we may need the values of multiple symbol
to be consistent, we can pass symbol
The static method provided for
method passes in the same descriptor to make their values consistent.
Symbol.for
This method searches the runtime symbol registry for an existing symbol using the given key and returns it if found. Otherwise, a new symbol is created in the global symbol registry using this key.
const sa=Symbol.for('cc') const sb=Symbol.for('cc') console.log(sa===sb); //true
Symbol.keyFor
This method is used to obtain the descriptor of the global symbol
.
const key =Symbol.keyFor(sb) console.log(key); // c
2. Set
Set
object (similar to an array) allows you to store any data type, but the Value cannot be repeated.
const s1 = new Set() s1.add(10) s1.add(20) s1.add(30) s1.add(40) console.log(s1) // Set(4) { 10, 20, 30, 40 } s1.add(20) console.log(s1) // Set(4) { 10, 20, 30, 40 }
Set common methods
Method | Return value | Description |
---|---|---|
size |
set The number in the object |
Returns the number in the set object Quantity |
add |
Set Object |
Add element |
delete |
boolean |
Delete element |
has |
boolean |
Set Whether this value exists in the object |
clear |
None | Clear the value in the Set object |
##3. WeakSet
WeakSet is another data structure similar to
Set, and the internal data cannot have duplicate values.
- The difference between it and
- Set
- WeakSet
can only store object types, not basic data types
- WeakSet
It is a weak reference to the element
- WeakSet
Basic use
const weakSet = new WeakSet(); let obj = { name: "_island" }; weakSet.add(obj);
WeakSet common methods
Return value | Description | |
---|---|---|
add
|
weaksetObject
| Add element|
delete
|
boolean
| Delete element|
has
|
boolean
|
weaksetWhether this value exists in the object
|
方法 | 返回值 | 说明 |
---|---|---|
get |
获取对应的元素 | 通过key 获取对应元素 |
size |
Map 对象中的数量 |
返回Map 对象中的数量 |
set |
Map 对象 |
添加元素 |
delete |
boolean |
删除元素 |
has |
boolean |
Set 对象中是否存在这个值 |
clear |
无 | 清空Set 对象中的值 |
遍历Map
通过foreach
语句遍历Map
map2.forEach((item) => console.log(item));
通过for..of
遍历Map
for ([val, key] of map2) { console.log(`${key}---${val}`); }
5、WeakMap
和Map
类似,也是以键值对的形式存在的
- 和Map的区别
-
WeakMap
的key
只能使用对象,不接受其他的类型作为key
-
WeakMap
的key
对对象是弱引用
-
基本使用
const weakMap = new WeakMap(); weakMap.set(obj, "a"); console.log(weakMap.get(obj)); // a
WeakMap常用方法
方法 | 返回值 | 说明 |
---|---|---|
get |
weakmap 对象 |
获取元素 |
delete |
boolean |
删除元素 |
has |
boolean |
weaksmap 对象中是否存在这个值 |
关于遍历
和WeakSet
一样,正因为它是弱引用,WeakMap
的key
是不可枚举的,如果key
可枚举那其列表将会受GC
影响。
【相关推荐:javascript视频教程、web前端】
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