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Examining various algorithms for string reversal.

NOTE: some of the methods, using recursion, have upper bounds on how long the string to be reversed can be, before the engine/browser will fail by running out of stack space for the recursion. Use recursion with caution.

Preparation code

<script>
  var test_str = "",
      tmp;
  
  for (var i = 0; i < 3000; i++) {
   test_str += String.fromCharCode((i % 26) + 97);
  }
  
  function string_reverse_1(str) {
   var new_str = "";
   for (var i = str.length - 1; i >= 0; i--) {
    new_str += str.charAt(i);
   }
   return new_str;
  }
  
  function string_reverse_2(str) {
   if (str.length < 1) return "";
  
   str = str.split(""); // make the string an array!
   var tmp, len = str.length,
       half_index = Math.floor(len / 2) - 1;;
   for (var i = 0; i <= half_index; i++) {
    tmp = str[len - i - 1];
    str[len - i - 1] = str[i];
    str[i] = tmp;
   }
  
   return str.join(""); // make the array a string again
  }
  
  function string_reverse_3(str) {
   return str.split("").reverse().join("");
  }
  
  function string_reverse_4(str) {
   if (str.length < 2) return str;
   return string_reverse_4(str.substr(1)) + str.charAt(0);
  }
  
  function string_reverse_5(str) {
   if (str.length < 2) return str;
  
   var half_index = Math.ceil(str.length / 2);
   return string_reverse_5(str.substr(half_index)) + string_reverse_5(str.substr(0, half_index));
  }
</script>

Test runner

Warning! For accurate results, please disable Firebug before running the tests. (Why?)

Java applet disabled.

tmp = "1" + string_reverse_1(test_str);

tmp = "2" + string_reverse_2(test_str);

tmp = "3" + string_reverse_3(test_str);

tmp = "4" + string_reverse_4(test_str);

tmp = "5" + string_reverse_5(test_str);

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Revisions

You can edit these tests or add even more tests to this page by appending /edit to the URL. Here’s a list of current revisions for this page:

• Revision 1: published by Kyle Simpson on 26th May 2011
• Revision 2: published on 26th May 2011
• Revision 3: published by Pointy on 26th May 2011
• Revision 4: published on 26th August 2011
• Revision 5: published on 10th November 2011

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