Improve startup performance.

jsdom’s require performance is quite slow. It takes about 500ms on my MBP" and it is the slowest part in Jest’s startup. If we could reduce this to 100ms, that would be super awesome.

Example:

console.time('jsdom');
require('jsdom');
console.timeEnd('jsdom');
jsdom: 490.010ms

Could we try to compile jsdom with inline-requires ( https://github.com/facebook/fbjs/blob/master/scripts/babel-6/inline-requires.js )? It has helped facebook.com’s startup performance. This of course is only useful if a lot of things in jsdom are required but not used when creating an instance of jsdom.

[ForbesLindesay]

A very brief investigation seems to suggest that we can cut ~80ms from cssstyle/lib/CSSStyleDeclaration.js’s time to require by inlining all the css properties. I’m going to see if I can build something a little bit more thorough though.

[SagnikPradhan]

I wonder, does bundling with rollup make any difference?