CODE EXAMPLE FOR JAVASCRIPT

two sum js

function twoSum(nums, target) {
    const viewed = []; // access by index is faster that Map
    for(let i=0; ;i++){ //according to task description - solution is always present - no need to check <.length or something like this
        const current = nums[i];
        const j = viewed[current];
        if(j !== undefined){
            return [i, j];
        }

        viewed[target - current] =  i; 
    }
};