SOURCE

const testArray1 = [1,2,3,4,5,6,7];
const testArray2 = [3,5,7,9,10,23];

function merge(arr1, arr2) {
  const newArray = [];
  let i = 0; j = 0;
  while(i<arr1.length && j<arr2.length) {
    const min = arr1[i] < arr2[j] ? arr1[i++]:arr2[j++];
    newArray.push(min);
  }
  
  while(i<arr1.length) {
    newArray.push(arr1[i++]);
  }
  while(j<arr2.length) {
    newArray.push(arr2[j++]);
  }
  return newArray;
}

console.log(merge(testArray1, testArray2))