Shaving Bytes with JavaScript Booleans

By  on  

Developers are always search for ultimate way to create something with the least amount of code.  This, of course, is one of the reasons we use minifiers: to serve code as small as possible.  Of course this practice has numerous benefits, like faster download time, less storage consumption, etc.  One way that minifiers are able to shave bytes off of JavaScript code is changing the way booleans are used.

true === !0 // Save 2 chars

false === !1 // Save 3 chars

A few bytes of every true and false go away with the ! evaluation.  If you set one-letter variables names to those values, you may end up saving more.  Keep in mind I'm not telling you to do this in your source code -- minifiers like Uglify JS will do this for you.  Just something neat to know about though!

Recent Features

  • By
    6 Things You Didn’t Know About Firefox OS

    Firefox OS is all over the tech news and for good reason:  Mozilla's finally given web developers the platform that they need to create apps the way they've been creating them for years -- with CSS, HTML, and JavaScript.  Firefox OS has been rapidly improving...

  • By
    Camera and Video Control with HTML5

    Client-side APIs on mobile and desktop devices are quickly providing the same APIs.  Of course our mobile devices got access to some of these APIs first, but those APIs are slowly making their way to the desktop.  One of those APIs is the getUserMedia API...

Incredible Demos


  1. Glad you aren’t advocating coding like this directly. Can’t beat true/false for readability.

  2. Roman

    Coercions like Number to Boolean doesn’t affect performance?

  3. Maybe too simple of a test:

    Looks like using !0 and !1 may be faster (in Chrome 35) but only marginally.

    • MaxArt

      Even if that’s true, and it’s not due to some statistical error, the gain is so small it’s not really worth it.

    • Those are noops anyway. I would be surprised if the JS engine just optimise them away at compile time.

    • didn’t just*

  4. Still prefer true/false for readability. As you said, it is better to let the Minifier to do this for us. It is better to keep the true/false in our code.

  5. I expect the gain to be lost as soon as the file gets gzipped. I am wrong?

  6. oresh

    You should also remember the bitwise operations like
    !~number, that returns true only for -1

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