30-seconds-of-code/snippets/js/s/replace-or-append-array-value.md

title, type, language, tags, author, cover, dateModified

title	type	language	tags	author	cover	dateModified
Replace or append array value	snippet	javascript	array	chalarangelo	boutique-home-office-2	2023-02-19T05:00:00-04:00

Replaces an item in an array or appends it, if it doesn't exist.

• Use the spread operator (...) to create a shallow copy of the array.
• Use Array.prototype.findIndex() to find the index of the first element that satisfies the provided comparison function, compFn.
• If no such element is found, use Array.prototype.push() to append the new value to the array.
• Otherwise, use Array.prototype.splice() to replace the value at the found index with the new value.

const replaceOrAppend = (arr, val, compFn) => {
  const res = [...arr];
  const i = arr.findIndex(v => compFn(v, val));
  if (i === -1) res.push(val);
  else res.splice(i, 1, val);
  return res;
};

const people = [ { name: 'John', age: 30 }, { name: 'Jane', age: 28 } ];
const jane = { name: 'Jane', age: 29 };
const jack = { name: 'Jack', age: 28 };
replaceOrAppend(people, jane, (a, b) => a.name === b.name);
// [ { name: 'John', age: 30 }, { name: 'Jane', age: 29 } ]
replaceOrAppend(people, jack, (a, b) => a.name === b.name);
// [
//   { name: 'John', age: 30 },
//   { name: 'Jane', age: 28 },
//   { name: 'Jack', age: 28 }
// ]