Pull values from array based on function

OSCC · JavaScript, Array · Oct 22, 2020

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.

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));
};

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

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