When you invoke the constructor function with new, the following happens inside the function:
• An empty object is created and referenced by this variable, inheriting the prototype of the function.
• Properties and methods are added to the object referenced by this.
• The newly created object referenced by this is returned at the end implicitly (if no other object was returned explicitly).
var Person = function (name) {
this.name = name;
this.say = function () {
return "I am " + this.name;
};
};
var adam = new Person("Adam");
adam.say(); // "I am Adam"
Note
reusable members, such as methods, should go to the prototype.
Person.prototype.say = function () {
return "I am " + this.name;
};
Constructor's Return Values
When invoked with new, a constructor function always returns an object inheriting from the constructor's prototype.
var Objectmaker = function () {
// this `name` property will be ignored
// because the constructor
// decides to return another object instead
this.name = "This is it";
// creating and returning a new object
var that = {};
that.name = "And that's that";
return that;
};
// test
var o = new Objectmaker();
console.log(o.name); // "And that's that"
You have the freedom to return any object in your constructors, as long as it's an object. Attempting to return something that's not an object (like a string or a boolean false, for example) will not cause an error but will simply be ignored, and the object referenced by this will be returned instead.