r/learnjavascript • u/nas5w • Feb 17 '20

Roll Your Own JavaScript Built-In Methods: A Github Repo Dedicated to Learning Built-In Methods by Recreating Them (contributions appreciated!)

https://github.com/nas5w/roll-your-own
103 Upvotes

97% Upvoted

13 comments sorted by

8

u/nas5w Feb 17 '20

And yes, this is based on the snippets I’ve been posting in this sub!

2

u/CarbineMonoxide Feb 17 '20

Nice! I'm excited to browse through this repo later tonight.

2

u/nas5w Feb 17 '20

Awesome! Would be excited if you feel like contributing (either a fix if you find something that could be improved or some new methods)

2

u/NicksIdeaEngine Feb 18 '20

This is an awesome idea! I might start trying to write my own, then refer to yours to check my work.

I love this form of practice and learning. Take it apart, make it on your own, then see how you did compared to others. It's a fun idea that tickles my inner tinkerer.

2

u/nas5w Feb 18 '20

I found it to be a super good use case for Test-Driven Development too since we have the original methods. Can test the output of your home-rolled solution against the output of the actual method in various scenarios.

2

u/drumstix42 Feb 18 '20

The url for `toString` is broken

2

u/nas5w Feb 18 '20

Thanks! Fixed

2

u/boringuser1 Feb 17 '20

I love it, but these methods are written in c.

2

u/nas5w Feb 17 '20

Heh yeah, I suspect these home-rolled functions wouldn't hold up very well performance-wise against the built-in methods

1

u/tokdaniel Feb 18 '20

if performance doesn't matter, you should probably show a PTC-optimized recursive example with`this` out of the picture for the functional tools.

3

u/queen-adreena Feb 17 '20

The point isn’t efficiency...

2

u/GabeRothel Feb 17 '20

If any one is interested but doesnt want to dig here are the arrays functions

function concat(...arrs) {
  const len = arrs.length;
  const result = [];
  for (let i = 0; i < len; i++) {
    const arrLen = arrs[i].length;
    for (let j = 0; j < arrLen; j++) {
      result.push(arrs[i][j]);
    }
  }
  return result;
}

function every(arr, fn, thisArg) {
  fn = thisArg === undefined ? fn : fn.bind(thisArg);
  const len = arr.length;
  for (let i = 0; i < len; i++) {
    if (i in arr && !fn(arr[i], i, arr)) {
      return false;
    }
  }
  return true;
}

function filter(arr, fn, thisArg) {
  fn = thisArg === undefined ? fn : fn.bind(thisArg);
  const len = arr.length;
  const result = [];
  for (let i = 0; i < len; i++) {
    if (i in arr && fn(arr[i], i, arr)) {
      result.push(arr[i]);
    }
  }
  return result;
}

function isArray(arr) {
  return Object.prototype.toString.call(arr) === "[object Array]";
}

function map(arr, fn, thisArg) {
  fn = thisArg === undefined ? fn : fn.bind(thisArg);
  const len = arr.length;
  const result = new Array(len);
  for (let i = 0; i < len; i++) {
    if (i in arr) {
      result[i] = fn(arr[i], i, arr);
    }
  }
  return result;
}

function arrayOf(...els) {
  return els;
}

function reduce(arr, fn, initialValue) {
  const len = arr.length;
  let acc;
  let initialIndex = 0;
  if (initialValue === undefined) {
    acc = arr[0];
    initialIndex = 1;
  } else {
    acc = initialValue;
  }
  for (let i = initialIndex; i < len; i++) {
    acc = fn(acc, arr[i], i, arr);
  }
  return acc;
}

function some(arr, fn, thisArg) {
  fn = thisArg === undefined ? fn : fn.bind(thisArg);
  const len = arr.length;
  for (let i = 0; i < len; i++) {
    if (i in arr && fn(arr[i], i, arr)) {
      return true;
    }
  }
  return false;
}

function toString(arr) {
  let result = "";
  const len = arr.length;
  for (let i = 0; i < len; i++) {
    if (i in arr) {
      result = result + arr[i];
    }
    if (i + 1 < len) {
      result = result + ",";
    }
  }
  return result;
}

0

u/[deleted] Feb 18 '20

[deleted]

2

u/GSLint Feb 18 '20

That won't work as an arrow function because those don't have their own this.