Why assign Math and document to local vars?

[adrianblynch]

Not an issue as much as a question...

Here you are assigning Math and document to _math and _document respectively, why is that?

https://github.com/phoboslab/underrun/blob/master/source/game.js#L3-L4

Thanks.

[phoboslab]

The build.sh concatenates all .js files and runs it through uglifyjs. Assigning global objects to local names helps uglifyjs to squeeze out a few extra bytes in the minified file if these objects are used often.

E.g. consider:

for (var i = 0; i < Math.PI*2; i+=0.1) {
	var x = Math.sin(r);
	var y = Math.cos(r);
	draw(x, y);
}

Will be minified to:

for(var a=Math,h=0;h<2*Math.PI;h+=.1){var t=Math.sin(r),M=Math.cos(r);draw(t,M)}

If we assign the global Math to a local var:

var _math = Math;
for (var i = 0; i < _math.PI*2; i+=0.1) {
	var x = _math.sin(r);
	var y = _math.cos(r);
	draw(x, y);
}

We will end up with:

for(var a=Math,v=0;v<2*a.PI;v+=.1){var d=a.sin(r),f=a.cos(r);draw(d,f)}

Maybe uglifyjs has a flag to do this automatically? I don't know. It worked out fine for my project, though.

[adrianblynch]

Thanks @phoboslab.

Really good game!