Math.xxx >50x slower in userscripts

Issue

calling Math.abs, Math.random, etc. is >50x slower in userscripts

test

to test just copy the following into a userscript open the site it is injected into, and paste the same into the console:

let acc = 0;
console.time("Math.randomx1000000");
for(let i=0; i<1000000; i++) acc += Math.random();
console.timeEnd("Math.randomx1000000");
console.time("Math.absx1000000");
for(let i=0; i<1000000; i++) acc += Math.abs(acc);
console.timeEnd("Math.absx1000000");

// result in userscript:
//   Math.randomx1000000: 4118.552978515625 ms
//   Math.absx1000000: 4082.463134765625 ms
// result in console:
//   Math.randomx1000000: 135.682861328125 ms
//   Math.absx1000000: 55.900634765625 ms

temporary fix

rebinding the object like this fixes the problem:

const Math = window.Math;

despite the simple fix, this caused me major issues (freezes when doing image manipulation) and headaches (took me way to long to debug, because the profiler just shows 40s spent with Math.abs being the only thing on that line)

speculation on the origin

I assume the property access somehow has overhead because of sand-boxing or something, but the Math object is indistinguishable from the normal one (no proxy, no funky getters / setters), so I have no clue what is going on.

[tophf]

I’ve implemented both tricks in #1532.

As for adaptive caching, I doubt it’s trivial so I’m afraid it’ll unnecessarily complicate code.

[RubenArtmann]

Just an Idea: you could count how many times each property gets used in the windowProxy and then dynamicly enable option 2 for everything where the overhead would be greater than 100ms on the next run.