CODEWITHSUNDEEP
javascript
lowerkey
lowerkey

Reputation: 8345

object oriented javascript how to create a static class for constants

I've decided to put all my constants in a neat class called constants, and would like to access its members with the dot operator.

So far I've tried:

function Constants(){
    Constants.style = {};
    Constants.style.border_sides = 20;
    Constants.style.button_width = 17;
    // ...
}

And later

Constants = new Constants();

and

{
    $('#button').width(Constants.style.button_width);
}

That resulted in a

Can't access button_width of undefined.

I would use JSON to declare the constants, but I like comments in my code. Would someone explain javascript's OO?

Upvotes: 4

Views: 5373

Answers (4)

Matt Greer
Matt Greer

Reputation: 62057

You replace the Constants function with an instance of Constants. And you applied your constants to the function, not an instance of Constants or the prototype. So you effectively wiped your constants away.

I'd argue just use an object literal

var constants = {
   style: {
        border_sides: 20
   }
};

Keep in mind there's nothing actually constant about either approaches. Anyone can easily change the "constant" values. If you want truly constant data, you might want to use getters/setters, Object.defineProperty or the module pattern.

Upvotes: 5

Abdul Munim
Abdul Munim

Reputation: 19217

Why don't you just consider using literals?

var Constants = {
    style: {
        border_sides: 20,
        button_width: 17
    }
}

Even if you are willing to consider using the construction function, replace Constants with this

function Constants(){
    this.style = {};
    this.style.border_sides = 20;
    this.style.button_width = 17;
    // ...
}

You don't need to do any new Constants() for literals (1st example). Just start using right away.

For 2nd example (constructor function) you need to do var constants = new Constants().

Upvotes: 4

Esailija
Esailija

Reputation: 140234

If you want a "class" with both static and instance methods:

function ClassName(){

}

ClassName.prototype = { //Put instance methods here
   instanceMethod1 : function(){},

   instanceMethod2 : function(){}
};

ClassName.staticMethod1 = function(){};
ClassName.staticMethod2 = function(){};

var a = new ClassName();

a.staticMethod1; //undefined
a.instanceMethod1; //function(){};

ClassName.staticMethod1 //function(){};

Upvotes: 5

Rich O'Kelly
Rich O'Kelly

Reputation: 41767

In Javascript everyting is an object, so you're adding properties to the Constants function within the function.

To get the effect you want write:

var Constants = {
  someText: 'text1',
  someInt: 1
};

And to access, is simply:

var text = Constants.someText;

Upvotes: 2

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