SOURCE

function twoSum(arr, target) {
    let map = new Map()
    for (let i = 0, len = arr.length; i < len; i++) {
        let k = target - arr[i]
        if (map.has(k)) {
            return [map.get(k), i]
        }

        map.set(arr[i], i)
    }
    return []
}


console.log(twoSum([2, 7, 11, 15], 13))