Increment number represented in Array

increment.js

/**
 * Increment number represented in array
 *
 * E.g. Take [1, 2, 3] increment to [1, 2, 4]
 * @param  {[Number]} arr Array to increment
 * @return {[Number]}     Array of numbers
 */
function increment(arr) {
  for(var i = arr.length - 1; i >= 0; i--) {
    if(arr[i] === 9) {
      arr[i] = 0;
      if(i === 0) {
        arr.unshift(1);
      }
    }
    else {
      arr[i] = arr[i] + 1;
      break;
    }
  }
  return arr;
}

console.log(increment([1, 2, 3, 4]));
console.log(increment([1, 2, 3, 9]));
console.log(increment([9, 9, 9]));
console.log(increment([0]));