JS symbol

Create a Symbol

// Create a symbol
const sym1 = Symbol();  //Primitive
const sym2 = Symbol('sym2');
console.log(typeof sym1);
console.log(sym2);


console.log(Symbol() === Symbol()); //false 都是独一无二的
console.log(Symbol(123) === Symbol(123)); //false 都是独一无二的

Symbol 转为string

console.log(`Hello ${String(sym1)}`);  //可以把symbol变为string
console.log(`Hello ${sym1.toString()}`); 

Symbol作为object的key

//Unique Object key
const KEY1= Symbol();
const KEY2= Symbol('sym2');

const myObj = {};

myObj[KEY1] = 'prop1';  //这样传入的key为symbol
// myObj.KEY1 = 'prop1'; //这样传入的名称为key1
myObj[KEY2] = 'prop2';
myObj.key3 = 'Prop3';
myObj.key4 = 'Prop4';

for…in不能遍历Symbol

//Symbols are not enumerable in for...in
for(let i in myObj){
  console.log(`${i}:${myObj[i]}`);  //只有key3和key4。不会遍历到symbol
}

JSON.stringify会忽略Symbol

//Json.stringify 会忽略symbol
//Symbols are ignored by JSON.stringify
console.log(JSON.stringify({key:'prop'}));
console.log(JSON.stringify({[Symbol('sym1')]:'prop'}));