Question

HI,

I have a JavaScript program that’s written with object literal syntax:

var MyJsProgram = {

    someVar: value1,
    somevar2: value2,

    init : function() {
        //do some initialisation
    },

    libraryFunction : function() {

    },

    getStyle : function() {

    },

    extend : function() {

    }
}

There can be multiple instances of this script running at once. Should I move the common methods in to the prototype object of the myJsProgram? If so, is this syntax correct?

 var MyJsProgram = {

    someVar: value1,
    somevar2: value2,

    init : function() {
        //do some initialisation
    },

    //more methods/members here that are unique to each instance
}

myJsProgram.prototype = {
    //all shared methods here
}

?

Answer 1

No, that syntax is not correct (no offense) 😉

You need to create an object for using its prototypes. That means that you need a constructor (which is a function in JavaScript). Applied to your problem:

var MyJsProgram = function (value1, value2) {
    // "this" refers to the current instance of this object
    this.someVar = value1;
    this.someVar2 = value2;
    // do some initialization
};

Create the new object like this:

var jsProgramInstance = new MyJsProgram(value1, value2);

Prototypes are instance members of those objects. They are defined like this:

MyJsProgram.prototype.someSharedMethodName = function () {
    // do shared method stuff here
    // (this.someVar and this.someVar2 are available here)
};

Use them like this (on your previously created instance):

jsProgramInstance.someSharedMethodName();

You should not do the following, since it overwrites the existing prototype properties that may exist (due to inheritance):

MyJsProgram.prototype = {
    someSharedMethodName: function () {
        // ...
    },
    // ...
};