cool!

It's best practice to minimize time complexity in case you're dealing with large amounts of data someday.

great minds think alike lol

I thought about it too xD

Just wanna say that sometimes, the program gives out an false but sometimes it gives all green, if you can fix it :)

Fact

I think the clearest form to use is by far this one

function name(args) {
  // whatever
}

Clearly the current version can be disturbing for a beginner, who may not be able to resolve the kata in one line. This is a 7kyu kata, aimed to complete novices.

A lot of ways to do a function

const startsWith = function(st, prefix) {
  // your code
};

It could also be:

const startsWith = (st, prefix) => {
  /* your code here */
}  

If you want to use ES6 style.

instead of making the user directly having a single line code is a little bit annoying for persons who starts, maybe instead of:

const startsWith = (st, prefix) => /* your code here */ true

put:

function startsWith(st, prefix) {
  // your code here
}

I wonder if I will get this level one day impressed

Because your code is wrong, it fails with 108 for example. Not a kata issue.

can someone explain me what means 'use strict' ? its there with northing before... don't understand, will love to have explanation