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
    Welcome to My New Office

    My first professional web development was at a small print shop where I sat in a windowless cubical all day. I suffered that boxed in environment for almost five years before I was able to find a remote job where I worked from home. The first...

  • By
    Responsive and Infinitely Scalable JS Animations

    Back in late 2012 it was not easy to find open source projects using requestAnimationFrame() - this is the hook that allows Javascript code to synchronize with a web browser's native paint loop. Animations using this method can run at 60 fps and deliver fantastic...

Incredible Demos

  • By
    Dynamically Load Stylesheets Using MooTools 1.2

    Theming has become a big part of the Web 2.0 revolution. Luckily, so too has a higher regard for semantics and CSS standards. If you build your pages using good XHTML code, changing a CSS file can make your website look completely different.

  • By
    Drag and Drop MooTools File Uploads

    Honesty hour confession:  file uploading within the web browser sucks.  It just does.  Like the ugly SELECT element, the file input is almost unstylable and looks different on different platforms.  Add to those criticism the fact that we're all used to drag and drop operations...

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!