/* This script and many more are available free online at
The JavaScript Source!! http://javascript.internet.com
Created by: Nannette T++++++ | http://www.shiningstar.net */
var checkflag = "false";
function check(field) {
  if (checkflag == "false") {
    for (i = 0; i < field.length; i++) {
      field[i].checked = true;
    }
    checkflag = "true";
    return "Uncheck All";
  } else {
    for (i = 0; i < field.length; i++) {
      field[i].checked = false;
    }
    checkflag = "false";
    return "Check All";
  }
}

<form name=myform action="" method=post> <table> <tr><td> <strong>Make a selection</strong><br> <input type=checkbox name=list value="1">Java<br> <input type=checkbox name=list value="2">JavaScript<br> <input type=checkbox name=list value="3">ASP<br> <input type=checkbox name=list value="4">HTML<br> <input type=checkbox name=list value="5">SQL<br> <br> <input type=button value="Check All" onClick="this.value=check(this.form.list)"> </td></tr> </table> </form>