I am in mid of my JavaScript session. Find this code in my coding exercise. I understand the logic but I didn't get this map[nums[x]] condition.

function twoSum(nums, target_num) {  

    var map = [];  

    var indexnum = [];  



    for (var x = 0; x < nums.length; x++)  

    {  

        if (map[nums[x]] != null)  

        // what they meant by map[nums[x]]

        {  

            index = map[nums[x]];  

            indexnum[0] = index+1;  

            indexnum[1] = x+1;  

            break;  

        }  

        else  

        {  

            map[target_num - nums[x]] = x;  

        }  

    }  

    return indexnum;  

    }  

console.log(twoSum([10,20,10,40,50,60,70],50));

I am trying to get the Pair of elements from a specified array whose sum equals a specific target number. I have written below code.

function arraypair(array,sum){

        for (i = 0;i < array.length;i++) {

            var first = array[i];

            for (j = i + 1;j < array.length;j++) {

                var second = array[j];



                if ((first + second) == sum) {

            alert('First: ' + first + ' Second ' + second + ' SUM ' + sum);

            console.log('First: ' + first + ' Second ' + second);

                }

            }



        }

}



var a = [2, 4, 3, 5, 6, -2, 4, 7, 8, 9];



arraypair(a,7);

Is there any optimized way than above two solutions? Can some one explain the first solution what exactly map[nums[x]] this condition points to?