JavaScript: Constructor Auto-Execution with new Keyword

By  on  

JavaScript is full of small, interesting facets that can trip you up, make you laugh, or make you cry.  This post is about an interesting one.  Those of you that have worked with JavaScript functions, and in a way JavaScript "classes" (as you used with MooTools), you're well acquainted with the new keyword.  With the new keyword you get the ability to pass arguments with the function call, but did you know that if you have no arguments, you don't need the parens at all?

function MyClass() {
	console.log('Initialized!');

	//Set a property, as an example
	this.dirty = true;
}

var instance = new MyClass;

// >> "Initialized!''

So why am I telling you this?  I have no idea.  It's just one of those fun tidbits that you can add to your brain. :)

Recent Features

  • By
    LightFace:  Facebook Lightbox for MooTools

    One of the web components I've always loved has been Facebook's modal dialog.  This "lightbox" isn't like others:  no dark overlay, no obnoxious animating to size, and it doesn't try to do "too much."  With Facebook's dialog in mind, I've created LightFace:  a Facebook lightbox...

  • By
    CSS 3D Folding Animation

    Google Plus provides loads of inspiration for front-end developers, especially when it comes to the CSS and JavaScript wonders they create. Last year I duplicated their incredible PhotoStack effect with both MooTools and pure CSS; this time I'm going to duplicate...

Incredible Demos

  • By
    Introducing MooTools Templated

    One major problem with creating UI components with the MooTools JavaScript framework is that there isn't a great way of allowing customization of template and ease of node creation. As of today, there are two ways of creating: new Element Madness The first way to create UI-driven...

  • By
    Create Snook-Style Navigation Using MooTools

    Jonathan Snook debuted a great tutorial last September detailing how you can use an image and a few jQuery techniques to create a slick mouseover effect. I revisited his article and ported its two most impressive effects to MooTools. The Images These are the same...

Discussion

  1. Amazing how the obvious is sometimes hidden in plain sight. I was going to save the extra () characters but it looks like there’s a micro performance hit in V8.

    http://jsperf.com/new-with-and-without-parens

    • MaxArt

      Really? That’s ironic, since Google Closure Compiler actually removes the parentheses when they can be omitted.

  2. Kostas Loupasakis

    That was something I always was curious about but never bothered to ask/look up. I assume the same thing also occurs in php?

  3. Asmor

    I’ll file this next to optional semi-colons and optional closing tags in HTML5: things that are interesting to know, but if I ever see while reviewing someone’s code I might get stabby.

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