Code:

/**
 * @param {number[]} nums
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(nums, target) {
    const map = new Map()

    for (let i = 0; i < nums.length; i++) {
        if (map.has(target - nums[i])) {
            return [map.get(target - nums[i]), i]
        }
        
        map.set(nums[i], i)
    }
};


console.log(twoSum([2,7,11,15], 9))
console.log(twoSum([3,2,4], 6))
console.log(twoSum([3,3], 6))