JavaScript原型上的toString到底是怎么运行的?大家来看看

[待解决问题]

alert(nf); // 5

为什么alert弹出的是5呢?

而console.log(nf); 却是numCount

我把numCount.prototype.toString改成numCount.prototype.toString1

alert就弹出[object Object]..

这是什么原因啊?

function numCount(){
                        var answer = 0;
                    }
                    numCount.prototype.addNumbers = function(num1,num2){
                            this.answer = num1 + num2;
                    }
                    numCount.prototype.toString = function(){
                            return this.answer;
                    }
                    var nf = new numCount();
                    nf.addNumbers(2,3);
                    console.log(nf);  // numCount
                    alert(nf);     // 5