SOURCE

//symbol 为数据提供一个独一无二的值
{
  let a1 =Symbol();
  let a2 =Symbol();
	//a1和a2永远都不会相等
  console.log(a1===a2);//false
	//但是另外一种方法可以
  let a3 = Symbol.for('a3');
  let a4 = Symbol.for('a3');
  console.log(a3===a4);//true
  //console.log(a3,a4);//是无法打印的
  console.log('-----')
}

{
  let a1=Symbol.for('abc');
  let obj={
    [a1]:'123',
    'abcd':345,
    'c':456,
  };
  console.log('obj',obj);
  
  for (let [key,value] of Object.entries(obj)){
    console.log('lot of', key,value);
  }
  
  Object.getOwnPropertySymbols(obj).forEach(function(item)){
    console.log(obj,[item]);
  }
	
	//拿到了symbol和非symbol的值
	Reflect.ownKeys(obj).forEach(function(item){
    console.log('ownKeys',item,obj[item]);
  })





}