How to find the two indices of numbers in an array that sum to a specific target

JavaScript, algorithms, arrays

Here is one way to find the two indices of numbers in an array that sum to a specific target:

twoSumTry in REPL
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function twoSum(a, b) {
  const obj = {};
    for (let i = 0; i < nums.length; i++) {
        const num = nums[i];
        if (obj[target-num] !== undefined) {
            return [obj[target-num], i];
        }
        obj[num] = i;
    }
    return [] // We can also throw an error here.
}