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

Incredible Demos

  • By
    CSS Fixed Positioning

    When you want to keep an element in the same spot in the viewport no matter where on the page the user is, CSS's fixed-positioning functionality is what you need. The CSS Above we set our element 2% from both the top and right hand side of the...

  • By
    Skype-Style Buttons Using MooTools

    A few weeks back, jQuery expert Janko Jovanovic dropped a sweet tutorial showing you how to create a Skype-like button using jQuery. I was impressed by Janko's article so I decided to port the effect to MooTools. The XHTML This is the exact code provided by...

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!