JSFiddle - React, Tailwind, and code Playground

JavaScript

function twoSum(array, sum) {
    const pairs = [];
    const store = [];

    for (let part1 of array) {
        const part2 = sum - part1;
        if (store.indexOf(part2) !== -1) pairs.push([part1, part2]);
        store.push(part1);
    }

    return pairs;
}

console.log(twoSum([1,2,2,3,4], 4));