ES6 knowledge points supplement

Symbol

symbol It is a kind of data type , Existing data types

Basic data type :

 character string 、 Boolean 、 Numbers 、null、undefined、symbol、bigInt( Greater than 9007199254740992 Number of numbers )

Reference data type ：

 object ( object 、 Array 、 function ) etc. 

Symbol.for() And Symbol() These two ways of writing , Will generate new Symbol

let sy = Symbol('a')
let sy1 = Symbol('a')
sy === sy1  // false

let s1 = Symbol.for('foo');
let s2 = Symbol.for('foo');
s1 === s2 // true

 As can be seen above ,Symbol Even if it is the same key, The number returned is also different .
Symbol.for() Pass value   It will determine whether the incoming value exists , If it doesn't exist , To return a new value .

class class

The first experience of class

   class Obj {
    
        constructor(one, two) {
    
          this.one = one;
          this.two = two;
        }
        hello() {
    
          console.log("hello");
        }
      }

      let obj = new Obj(1,2);
      obj.hello();
      console.log(obj);

hello
Obj {
    one: 1, two: 2}

constructor ( When instantiating ), Receive the value transmitted when instantiating , And then automatically constructor In itself .

Static member of class

      class Obj {
    
		
	  }  perhaps 
      function Obj() {
    
	
	  }
      Obj.name = "fujin";
      let obj = new Obj();
      console.log(obj); // An empty object , No attribute added 

because name Only belong to Obj This class or constructor , Does not belong to instance object , This is the static member of the class , If you want to instance objects, you can use name, It can be used Obj.prototype.name= "fujin"


Again , stay class in , If you use static keyword , So long is equivalent to Obj.name = ‘fujin’

 class Obj {
	static name = 'fujin'	
 }