Stopwatch

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Description:

This JavaScript allows you to start and stop a timer.

JavaScript Functions:
<script LANGUAGE="JavaScript"> var timerRunning = false var timerID = null // create instance of Date object representing current time var initial = new Date() // start timer function start_watch() { // set the button's label to "stop" document.forms['watch'].general.value = "stop" // assign the stop function reference to the button's onClick event handler document.forms['watch'].general.onclick = stop // ask the user if to reset the timer if (confirm("Would you like to reset the timer?")) // set global variable to new time initial = new Date() // assign milliseconds since 1970 to global variable startTime = initial.getTime() // make sure the timer is stopped stopTimer() // run and display timer showTimer() } // set button to initial settings function stop() { // set the button's label to "start" document.forms['watch'].general.value = "start" // assign the start_watch function reference to the button's onClick event handler document.forms['watch'].general.onclick = start_watch // stop timer stopTimer() } // stop timer function stopTimer() { // if the timer is currently running if (timerRunning) // clear the current timeout (stop the timer) clearTimeout(timerID) // assign false to global variable because timer is not running timerRunning = false } function showTimer() { // create instance of Date representing current timer var current = new Date() // assign milliseconds since 1970 to local variable var curTime = current.getTime() // assign difference in milliseconds since timer was cleared var dif = curTime - startTime // assign difference in seconds to local variable var result = dif / 1000 // is result is not positive if (result < 1) // attach an initial "0" to beginning result = "0" + result // convert result to string result = result.toString() // if result is integer if (result.indexOf(".") == -1) // attach ".00" to end result += ".00" // is result contains only one digit after decimal point if (result.length - result.indexOf(".") <= 2) // add a second digit after point result += "0" // place result in text field document.forms['watch'].display.value = result // call function recursively immediately (must use setTimeout to avoid overflow) timerID = setTimeout("showTimer()", 0) // timer is currently running timerRunning = true } </script>

HTML Script:
<form name="watch"> <input TYPE="text" NAME="display" onFocus="this.blur()" size="20"> <input TYPE="button" NAME="general" VALUE="start" onClick="start_watch();"> </form>