What are the data types that are not part of javascript?

The data type that does not belong to javascript is interface, which is a reserved word in js; and the data types of javascript include Undefined, Number, Symbol, etc.

The operating environment of this article: windows7 system, javascript version 1.8.5, Dell G3 computer.

The basic data types of JavaScript are: (1) Undefined, (2) Null, (3) Boolean, (4) String, (5) Number, (6) Symbol, ( 7) Object. ES6 adds the Symbol type. The following mainly talks about some related knowledge points of the Symbol type.

Characteristics of Symbol

1. The instance is unique and unchangeable; a unique identifier The symbol can be used as the unique attribute name of the object so that others will not overwrite or overwrite the attribute value you set.

1 let id = Symbol("id");

2. Characteristics of data types: uniqueness, even if the values ​​generated by the same variable are not equal.

1 let id1 = Symbol("id");2 let id2 = Symbol("id");3 console.log(id1 == id2);  //false

3. Characteristics of data types: Hiddenness, for···in, object.keys() cannot be accessed.

1 let id = Symbol("id");2 let obj = {3     [id] : 'symbol'          
4 }5 for ( let key in obj){6     console.log(obj[key]);  //输出为空7 }

Accessible methods: Object.getOwnPropertySymbols, will return an array whose members are all functions of the current object Symbol value of the attribute name.

1 let id = Symbol("id");2 let obj = {3   [id] : 'symbol'      
4 }5 let arr = Object.getOwnPropertySymbols(obj);6 console.log(arr)  // [Symbol(id)]7 console.log(obj[arr[0]]) // 'symbol'

4. The same symbol value can be used multiple times. The official provides a global registration and registration method: Symbol.for()

let name1 = Symbol.for("name"); // 检测未创建后新建let name2 = Symbol.for("name"); // 检测已创建后返回console.log(name1 == name2); // true

In this way, you can get the global symbol object through the parameter value. On the contrary, you can use Symbol.keyFor()Get the parameter value.

let name1 = Symbol.for("name");
let name2 = Symbol.for("name");
console.log(Symbol.keyFor("name1")); // 'name'console.log(Symbol.keyFor("name2")); // 'name'

5. The result of instanceof is false

let s = Symbol('foo');
console.log(s instanceof Symbol); // false

Note: The parameters when creating symbol type data are just Used as an identifier, so Symbol() can also be used as a parameter.

[Recommended learning: javascript advanced tutorial]

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