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Shaving Bytes with JavaScript Booleans

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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!

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Discussion

  1. DesigNinja.net

    Cool :-)

  2. kyle

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

  3. Roman

    Coercions like Number to Boolean doesn’t affect performance?

  4. Mitchell Simoens

    Maybe too simple of a test: http://jsperf.com/bool-num-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.

    • Petah

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

    • Petah

      didn’t just*

  5. Teylor Feliz

    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.

  6. Arnaud Rinquin

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

  7. oresh

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

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