Access JavaScript Object Variable Properties

By  on  

Not all JavaScript objects are as easy as MyObject.property. Sometimes you may want to access a property whose key is stored in a variable. Luckily accessing these properties is very easy.

Javascript Object Property Accessing Example

/* setting */
var myObject = {
	left : 30,
	top: 20
};
/* basic access */
var left = myObject.left; //OR
var left = myObject['left'];

/* accessing it or variables */
var mode = 'vertical';
var value = myObject[mode == 'horizontal' ? 'left' : 'top'];

You may use array-style syntax to access an object's properties. The string within brackets returns the properties.

Recent Features

  • By
    Create a CSS Flipping Animation

    CSS animations are a lot of fun; the beauty of them is that through many simple properties, you can create anything from an elegant fade in to a WTF-Pixar-would-be-proud effect. One CSS effect somewhere in between is the CSS flip effect, whereby there's...

  • By
    Designing for Simplicity

    Before we get started, it's worth me spending a brief moment introducing myself to you. My name is Mark (or @integralist if Twitter happens to be your communication tool of choice) and I currently work for BBC News in London England as a principal engineer/tech...

Incredible Demos

  • By
    Basic AJAX Requests Using MooTools 1.2

    AJAX has become a huge part of the modern web and that wont change in the foreseeable future. MooTools has made AJAX so simple that a rookie developer can get their dynamic pages working in no time. Step 1: The XHTML Here we define two links...

  • By
    Fading Links Using jQuery:  dwFadingLinks

    UPDATE: The jQuery website was down today which caused some issues with my example. I've made everything local and now the example works. Earlier this week, I posted a MooTools script that faded links to and from a color during the mouseover and mouseout events.

Discussion

  1. I’m a big fan of myObject[key] as its close to the PHP array syntax. Just personal preference really and it gives great flexibility and easy to test for.

  2. @Colin – I just love how object property keys and array indexes are treated as equal in Javascript. The closest to this coolness that PHP comes is in pseudo-property keys ($obj->$var_key)

  3. dev

    never knew this method, very useful.

  4. @Chris – PHP’s ArrayObject class allows you to access properties using array syntax.

  5. @keith – huh…never knew that. Thanks! :D

  6. It’s a good thing to point out that you can almost always avoid eval() by use of myObject[‘key’] reference. for example:

    var myObject = {};
    
    $H({
         'a': 1,
         'b': 2,
         'c': 3
    }).each(function(v, k) {
         myObject[k] = v;
    });
    

    A lot of people think you have to do something like:

    var myObject = {};
    
    $H({
         'a': 1,
         'b': 2,
         'c': 3
    }).each(function(v, k) {
         eval('myObject.' + k + ' = ' + v);
    });
    

    Avoid eval! Eval is evil.

  7. @Timothy: While it is preferable to avoid eval in code that need not be written in that form, as you show, I would like to contest that eval is far from evil.

    It’s a basic language construct upon which the entire functional programming paradigm can be built in languages that do not support it natively. Sometimes a problem is better expressed in said paradigm, but the language prevents you from properly exploiting it’s capabilities. This is one of the many ways eval *can* be used for the better of your programming speed, debug-ability and general style of programming.

    So please, next time you wish to share your opinion on eval, try to think of the grand picture this language construct fits in, and don’t spread lies about otherwise finely crafted implementations thereof.

  8. Thank you! I was stumped but this got me back on track.

  9. Ik

    Thank you soooo much, didn’t know this was possible. Spent countless hours trying to refactor my object to make calls easier, wish someone told me about this earlier lol.

Wrap your code in <pre class="{language}"></pre> tags, link to a GitHub gist, JSFiddle fiddle, or CodePen pen to embed!