为什么在JavaScript原型中返回“ this”会导致循环

Question

So I have this super simple JS Object I was messing around with and I came across something I can't figure out. When I run this, obj.toString is called over and over until I receive a 'Maximum call stack size error'. However, if I replace 'this' in the obj.type return to 'this.name', everything works fine. I realize I wouldn't normally return just 'this', but why is it getting caught in a loop when I do?

var Dog = function(name){
  this.name = name;
}
Dog.prototype.type = function(){
  return this;
}
Dog.prototype.toString = function(){
  //console.log(this.type())

  return "Dog's name: " + this.type();
}

var spot = new Dog('spot');
console.log(spot.toString());

Answer 1

When you stringify an object in javascript, the toString() function is called.

In this case, you have a custom toString() function. Cool.

So let's trace this:

1. console.log(spot.toString())
2. return "Dog's name: " + this.type();
3. return this;
4. // Hmmmm. How do we add "this" to our string. Easy we call toString().
5. return "Dog's name: " + this.type();
6. return this;
7. // Hmmmm. How do we add "this" to our string. Easy we call toString().
8. return "Dog's name: " + this.type();
9. return this;

Uh oh....

Answer 2

I believe your return statement in the toString method should be return "Dog's name: " + this.name; .

Answer 3

var Dog = function(name){
  this.name = name;
}
Dog.prototype.type = function(){
  return this;
}
Dog.prototype.getName = function(){
  //console.log(this.type())

  return "Dog's name: " + this.type(); // <- Calls toString method
}
Dog.prototype.toString = function(){
    return this.name;
};

var spot = new Dog('spot');
console.log(spot.getName());