对象的valueOf和toString

var a = {
    valueOf : function () {
      return 10;
    },
    toString: function () {
        return 'this is tostring';
    }
}

//print this object a
console.log(a)

//20
console.log(a+10);

//this is tostrig10
delete a.valueOf;
console.log(a+10);

 

来源：oschina

链接：https://my.oschina.net/u/2285087/blog/3184907