Two Sum

TwoSum.js

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
  for (let i = 0; i < nums.length; i++) {
    const firstNumber = nums[i];
    const secondNumberIndex = nums.slice(i+1).indexOf(target - firstNumber) + i + 1;

    if (secondNumberIndex > i) return [i, secondNumberIndex];
  }
};