编辑代码

let s1 = Symbol("foo")
let s2 = Symbol("bar")
console.log(s1,s2)
const obj = {
    toString(){
        return 'abc'
    }
}
const sym = Symbol(obj)
console.log(sym)
console.log(String(sym),sym.toString())
let s3 = Symbol()
console.log(Boolean(!s3))
console.log(s1.description)
//Symbol可以转为布尔值，显示的转为字符串

let mySymbol = Symbol()
let test = Symbol()
// let a ={}
// a[mySymbol] = 'Hello!';

// console.log(a)
// 将Symbol作为对象key的标识符，来使得key唯一
let a = {
    [mySymbol]:'Hello!',
    [test](arg){
        console.log('test',arg)
    }
}
console.log(a[mySymbol])
a[test](222)

const COLOR_RED    = Symbol('COLOR_RED');
const COLOR_GREEN  = Symbol('COLOR_GREEN');

function getComplement(color) {
  switch (color) {
    case COLOR_RED:
      return COLOR_GREEN;
    case COLOR_GREEN:
      return COLOR_RED;
    default:
      throw new Error('Undefined color');
    }
}
console.log(getComplement(COLOR_RED))


const shapeType = {
  triangle: 'Triangle'
};

function getArea(shape, options) {
  let area = 0;
  switch (shape) {
    case shapeType.triangle:
      area = .5 * options.width * options.height;
      break;
  }
  return area;
}

console.log(getArea(shapeType.triangle,
 { width: 100, height: 100 }));