gistfile1.txt

  function immutable(originalArray) {
      // Instead of mutating/modifying the original array,
      // we first make a copy of the original array
      // In this way, the original array stay unchanged.
      var newArray = [...originalArray];
      newArray[0] = "new value";
      return newArray;
  }

  var array = ["some value", "another value"];
  alert("Return from immutable " + immutable(array));
  alert("Array: " + array + " (original array stay unchanged).");