Find 2 numbers in an array input that up add to a target number and return their indices

twoSum.ts

/**
 * Given an array of integers, return indices of the two numbers such that they add up to a specific target.
 * You may assume that each input would have exactly one solution, and you may not use the same element twice.
 *
 * @param {Array<number>} nums
 * @param {number} target
 * @return {Array<number>}
 */
const nums: Array<number> = [3, 5, 8, 15, 22, 78]
const target: number = 30

const twoSum = function(nums: Array<number>, target: number): Array<number> | undefined {
    // look up set
    // loop over the input array
    // Evaluate if the lookup hash has a property equating to current index's value
    // if true, return an array containing this propertie's index value along with current loop index.
    // else add the current index value to lookup hash table and assign its index
    
    let lookup: object = {}
    
    for (let i = 0; i < nums.length; i++) {
        // lookup.hasOwnProperty(lookup[30-3]) --- false
        // lookup.hasOwnProperty(lookup[30-5]) --- false
        // lookup.hasOwnProperty(lookup[30-8]) --- false
        // lookup.hasOwnProperty(lookup[30-15]) --- false
        // lookup.hasOwnProperty(lookup[30-22]) --- true
        if (lookup.hasOwnProperty([target - nums[i]])) {
            return [lookup[target - nums[i]], i] // [2, 4]
        }
    
        // lookup[3] = 0 // { 3: 0 }
        // lookup[5] = 1 // { 3: 0, 5: 1 }
        // lookup[8] = 2 // { 3: 0, 5: 1, 8: 2 }
        // lookup[15] = 3 // { 3: 0, 5: 1, 8: 2, 15: 3 }
        lookup[nums[i]] = i
    }
};

twoSum(nums, target) // result: [2, 4]