CODEWITHSUNDEEP
javascriptvideoh.264modernizr
programbyexception
programbyexception

Reputation: 355

Modernizr and Video.h264

I am looking at how Modernizr detects support for Video and H.264, but it does not make any sense to me. Isn't bool a primitive boolean? why does it become a Boolean object? Why does bool.h264 magically start making any sense at all? thanks

tests['video'] = function() {
        var elem = document.createElement('video'),
            bool = false;

        // IE9 Running on Windows Server SKU can cause an exception to be thrown, bug #224
        try {
            if ( bool = !!elem.canPlayType ) {
                bool      = new Boolean(bool);
                bool.ogg  = elem.canPlayType('video/ogg; codecs="theora"')      .replace(/^no$/,'');

                // Without QuickTime, this value will be `undefined`. github.com/Modernizr/Modernizr/issues/546
                bool.h264 = elem.canPlayType('video/mp4; codecs="avc1.42E01E"') .replace(/^no$/,'');

                bool.webm = elem.canPlayType('video/webm; codecs="vp8, vorbis"').replace(/^no$/,'');
            }

        } catch(e) { }

        return bool;
    };

Upvotes: 2

Views: 343

Answers (2)

levi
levi

Reputation: 25111

Initially bool is indeed a primitive boolean, which cannot have properties added to it. Following the if condition, the value of bool gets overwritten via new Boolean(bool). In Javascript, calling new on a function, creates an empty Object, and uses the function as a constructor for said object. In the case of the Boolean() constructor, the only notable addition to the object, is a valueOf() function which returns the original primitive value. Otherwise, you now have a normal Object which can have arbitrary properties added to it.

See here and here.

Upvotes: 3

Patrick
Patrick

Reputation: 13974

I actually wrote a majority of that test.

That is just the format that Modernizr has followed for detects with sub values. In JavaScript, everything is an object, and new Boolean is as well.

Upvotes: 2

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