SOURCE

var matrixReshape = function(nums, r, c) {
    let pR = nums.length, pC = nums[0].length;
    if (pR * pC != r * c) {
        return nums;
    }
    let newArr = [], resultArr = [], count = 0;
    for (var value of nums) {
      newArr.push(...value);
    }
    console.log(newArr)
    for (let i = 0; i < r; i++) {
        let currArr = [];
        for (let j = 0; j < c; j++) {
            currArr.push(newArr[count]);
            count ++;
        }
        resultArr.push(currArr);
    }
    return resultArr;
};
let nums = [[1,2,3,4]];
console.log(matrixReshape(nums, 2, 2))