LeetCode 1570. Dot Product of Two Sparse Vectors

My solution in JavaScript:

/**
 * @param {number[]} nums
 * @return {SparseVector}
 */
 var  SparseVector   = function (nums ) {
     const  x   = new  Map ()
     for  ( let  i   =   0 ; i   <  nums .length ; i  ++ ) {
         if  (nums [i ]  !=   0 ) {
            x .set (i , nums [i ])
        }
    }
     this.map   =  x
     this.length   =  nums .length
     return this
};


// Return the dotProduct of two sparse vectors
/**
 * @param {SparseVector} vec
 * @return {number}
 */
SparseVector .prototype .dotProduct   = function (vec ) {
     let  ans   =   0 ;

     for  ( let  i   =   0 ; i   <  vec .length ; i  ++ ) {
         if  (vec .map .has (i )  && this.map .has (i )) {
            ans   +=  vec .map .get (i )  * this.map .get (i )
        }
    }

     return  ans
};

// Your SparseVector object will be instantiated and called as such:
// let v1 = new SparseVector(nums1);
// let v2 = new SparseVector(nums2);
// let ans = v1.dotProduct(v2);