SOURCE

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

let nums = [2,9,7]
let target = 9

console.log(sumIndex(nums,target))