---
title: Pull values from array based on function
type: snippet
language: javascript
tags: [array]
cover: book-chair
dateModified: 2020-10-22T20:24:04+03:00
---

Mutates the original array to filter out the values specified, based on a given iterator function.

- Check if the last argument provided is a function.
- Use `Array.prototype.map()` to apply the iterator function `fn` to all array elements.
- Use `Array.prototype.filter()` and `Array.prototype.includes()` to pull out the values that are not needed.
- Set `Array.prototype.length` to mutate the passed in an array by resetting its length to `0`.
- Use `Array.prototype.push()` to re-populate it with only the pulled values.

```js
const pullBy = (arr, ...args) => {
  const length = args.length;
  let fn = length > 1 ? args[length - 1] : undefined;
  fn = typeof fn == 'function' ? (args.pop(), fn) : undefined;
  let argState = (Array.isArray(args[0]) ? args[0] : args).map(val => fn(val));
  let pulled = arr.filter((v, i) => !argState.includes(fn(v)));
  arr.length = 0;
  pulled.forEach(v => arr.push(v));
};
```

```js
var myArray = [{ x: 1 }, { x: 2 }, { x: 3 }, { x: 1 }];
pullBy(myArray, [{ x: 1 }, { x: 3 }], o => o.x); // myArray = [{ x: 2 }]
```