使用文字和自定义构造函数创建Javascript对象

Question

I understand that there are multiple ways to create an object in javascript and I have been reading that object literal syntax is generally preferred. (Correct?)

What I haven't been able to figure out is if there is ever a reason to use any of the other ways to create objects, such as a custom constructor function ( var p = new Person("Adam") )? Is it true to use a custom constructor function only if I want private variables or to add methods or properties to its prototype? Is there no way to do these in a literal?

Answer 1

The discussion usually is about to prefer

var myObject = {};

over

var myObject = new Object();

If you however create your own constructor functions you are perfectly allowed to instantiate them with the new keyword, nothing controversial there.

Answer 2

You can use the custom constructor function when you want to create instances of objects, similar to Java.

For example:

function MyObj(x){
   this.x = x;
}

MyObj.prototype.printX = function(){
   alert(this.x);
}

var obj1 = new MyObj("hello");
var obj2 = new MyObj("hello2");
obj1.printX();//prints hello
obj2.printX();//prints hello2

Now I have two instances of this object. If I used String literals I would need to clone the object into a new var in order to get another instance.

Answer 3

The preferred method would be to use JSON: var p = { "name":"Adam" };

If you have a lot of member variables you need to initialize, or will be using a lot of objects (such as an array of them), etc. then it only makes sense to go ahead and create a function (constructor) which will do all of this for you. Unless you want your code to look like this:

var a = { "name":"Adam", "age":23, "city":"Boston" };
var b = { "name":"Jeff", "age":24, "city":"San mateo" };
var c = { "name":"Aaliyah", "age":25, "city":"New York" };
var d = { "name":"Mary", "age":26, "city":"Dallas" };