Discussion on: 9 Extremely Powerful JavaScript Hacks

I wanted to point out that #9 (using length to empty an array) is particularly useful if you are using ES6+ syntax and declaring your arrays with const instead of var. This keeps you from having to declare your array with let just to empty it.

I also wanted to share that according to tests I ran using several benchmarking tools, it is slightly faster on some browsers to convert a string to a number by multiplying it by 1 then by using the + operator as you do in #4:

const stringNum = "256.3"
const number = stringNum * 1;
console.log(number); // Logs 256.3

The difference is pretty negligible though. The fastest three methods were all very close in speed. Your method, the above method of multiplying by 1, and in a close third is using the Number constructor:

const number = Number(stringNum);

Here are another couple of quick things I've picked up.

A more performant and shorter replacement for Math.trunc(num) and parseInt(num), as well as working as a replacement for Math.floor(num) if you know the number won't be negative, using bitwise operator. This works on numbers stored as strings as well as regular numbers:

const num = 568.328;
const strNum = "243.782";

const truncatedNum1 = num|0;
const truncatedNum2 = strNum|0;

console.log(truncatedNum1); // Logs 568
console.log(truncatedNum2); // Logs 243

A more performant, albeit limited, way to fix a number to a single decimal place rather than use the incredibly slow num.toFixed(1):

const fixToOne = num =>
  (num = Math.round(num * 10) / 10) + (num === (num|0) ? '.0' : '');

fixToOne(2.3892); // Returns "2.4"

You can change the function by wrapping the returned value in parens and multiply by 1 at the end if you need a number returned rather than a string, but toFixed() returns a string so that's what I decided to return too.

A more performant but limited way to fix a number to two decimal places rather than use the incredibly slow num.toFixed(2):

const fixToTwo = num => 
  (num = (Math.round(num * 100) / 100) +
  (num === (num|0) ? '.0' : 0)) + (num === (num|0) ? '.0' : '') +
  (num * 10 === ((num * 10)|0) ? '0' : '');

fixToTwo(2.3892); // Returns "2.39"

You can see the benchmarks on these custom functions versus the native toFixed() and witness how drastic the speed difference is here: jsperf.com/decimal-rounding-tofixe...