old_contents: function append (arr1, arr2) {
    if (arr2 == null) return arr1
  
    var len1 = arr1.length
    var len2 = arr2.length
    var i = -1
  
    while (++i < len2) {
      arr1[len1 + i] = arr2[i]
    }
    return arr1
  }
  
  module.exports = append
  
new_contents: // Appends an array to the end of the other.
  // The first array will be modified and will contain the appended items.
  
  function append (arr1, arr2) {
    if (arr2 == null) return arr1
  
    var len1 = arr1.length
    var len2 = arr2.length
    var i = -1
  
    while (++i < len2) {
      arr1[len1 + i] = arr2[i]
    }
    return arr1
  }
  
  module.exports = append
  
subject: comment array/append.js