JSFiddle - React, Tailwind, and code Playground

JavaScript

var moveToStart = function(input) {
  var n = input.length - 1;
  var count = n;
  for (var i = n - 1; i >= 0; i--) {
    if (input[i] !== 0) {
      input[count--] = input[i];
    }
  }
  while (count >= 0) {
    input[count--] = 0;
  };
  return input;
};

var moveToEnd = function(input) {
  var n = input.length;
  var count = 0;
  for (var i = 0; i < n; i++) {
    if (input[i] !== 0) {
      input[count++] = input[i];
    }
  }
  while (count < n) {
    input[count++] = 0;
  };
  return input;
};

var arr = [3, 2, 0, 1, 5, 0, 0];
arr = moveToStart(arr);
for (var i = 0; i < arr.length; i++) {
  console.info(arr[i]);
}
console.log();
arr = moveToEnd(arr);
for (var i = 0; i < arr.length; i++) {
  console.info(arr[i]);
}