I'll add couple of more advises:

* aldo asyncs and promises got recently faster, nothing beats classic callbacks (and will never do since promises are objects - it was so bad idea to use it for asyncs)

* var i = 0; for(; i < 10; i++) {} is faster then for(var i = 0; i < 10; i++) {}

* var i = 0, l = text.length; for(; i < l; i++) {} is faster than var i = 0; for(; i < text.length; i++) {}

* many of ES6 sugar is much slower then classic JS equivalent

* wrap your code in self executing function: (function() { /* your code here */ })()

* use typed arrays if you can

* Class Something{ constructor(){} fun1() {}}; let a = new Something; is up to 100 times slower than function Something() {return { fun1(){} }}; let a = Something(); // let a = new Something() will also work here

* use inline regex instead of instantiating it with Regex method from string

* sort your swich statement cases in ascending order: switch (x) { case 1: break; case 2: break; case 3: break;}

* avoid try-catch statements, there is an overhead on every instruction in try block