JavaScript对象类型转换的分类及步骤详解

let obj = {
    name: 'jack',
    money: 1,
    [Symbol.toPrimitive](hint) {
      console.log(hint);
      return hint == 'string' ? this.name : this.money;
    },
  };
  let person = {
    jack: 'property jack',
  };
  // hint equals to string
  alert(obj);  // jack
  alert(person[obj]) // property jack
  // hint equals to number
  alert(+obj); // 1
  alert(obj > 0); // true
  // hint equals to default
  alert(obj + 50); // 51

let obj = {
    name: 'jack',
    money: 1,
  };
  // hint equals to string, excutes the toString() and return [object object]
  alert(obj); // [object object]
  // hint equals to number, excutes the valueOf() and return the object itself
  alert(+obj); // NaN  
  // hint equals to default, excutes the valueof() and return the object itself
  alert(obj === obj);  // true  // do the same as (obj.valueOf() === obj);

// if there exsits a toString(), and no other functions such as valueOf() or [symbol.toPromitive], then all the conversions will excute toString()
  let obj = {
    name: 'jack',
    money: 1,
    toString() {
      return  this.money;
    },
  };
  alert(obj); // 1
  alert(+obj); // 1 
  alert(obj + 9); // 10