Replace or append array value
JavaScript, Array · Feb 19, 2023
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 }
// ]
