You'll see the demo code is just a start/stop/reset millisecond counter. If you want to do fanciful formatting on the time, that's completely up to you. This should be more than enough to get you started.
This was a fun little project to work on. Here's how I'd approach it
var Stopwatch = function(elem, options) {
var timer = createTimer(),
startButton = createButton("start", start),
stopButton = createButton("stop", stop),
resetButton = createButton("reset", reset),
offset,
clock,
interval;
// default options
options = options || {};
options.delay = options.delay || 1;
// append elements
elem.appendChild(timer);
elem.appendChild(startButton);
elem.appendChild(stopButton);
elem.appendChild(resetButton);
// initialize
reset();
// private functions
function createTimer() {
return document.createElement("span");
}
function createButton(action, handler) {
var a = document.createElement("a");
a.href = "#" + action;
a.innerHTML = action;
a.addEventListener("click", function(event) {
handler();
event.preventDefault();
});
return a;
}
function start() {
if (!interval) {
offset = Date.now();
interval = setInterval(update, options.delay);
}
}
function stop() {
if (interval) {
clearInterval(interval);
interval = null;
}
}
function reset() {
clock = 0;
render(0);
}
function update() {
clock += delta();
render();
}
function render() {
timer.innerHTML = clock / 1000;
}
function delta() {
var now = Date.now(),
d = now - offset;
offset = now;
return d;
}
// public API
this.start = start;
this.stop = stop;
this.reset = reset;
};
// basic examples
var elems = document.getElementsByClassName("basic");
for (var i = 0, len = elems.length; i < len; i++) {
new Stopwatch(elems[i]);
}
// programmatic examples
var a = document.getElementById("a-timer");
aTimer = new Stopwatch(a);
aTimer.start();
var b = document.getElementById("b-timer");
bTimer = new Stopwatch(b, {
delay: 100
});
bTimer.start();
var c = document.getElementById("c-timer");
cTimer = new Stopwatch(c, {
delay: 456
});
cTimer.start();
var d = document.getElementById("d-timer");
dTimer = new Stopwatch(d, {
delay: 1000
});
dTimer.start();
.stopwatch {
display: inline-block;
background-color: white;
border: 1px solid #eee;
padding: 5px;
margin: 5px;
}
.stopwatch span {
font-weight: bold;
display: block;
}
.stopwatch a {
padding-right: 5px;
text-decoration: none;
}
<h2>Basic example; update every 1 ms</h2>
<p>click <code>start</code> to start a stopwatch</p>
<pre>
var elems = document.getElementsByClassName("basic");
for (var i=0, len=elems.length; i<len; i++) {
new Stopwatch(elems[i]);
}
</pre>
<div class="basic stopwatch"></div>
<div class="basic stopwatch"></div>
<hr>
<h2>Programmatic example</h2>
<p><strong>Note:</strong> despite the varying <code>delay</code> settings, each stopwatch displays the correct time (in seconds)</p>
<pre>
var a = document.getElementById("a-timer");
aTimer = new Stopwatch(a);
aTimer.start();
</pre>
<div class="stopwatch" id="a-timer"></div>1 ms<br>
<pre>
var b = document.getElementById("b-timer");
bTimer = new Stopwatch(b, {delay: 100});
bTimer.start();
</pre>
<div class="stopwatch" id="b-timer"></div>100 ms<br>
<pre>
var c = document.getElementById("c-timer");
cTimer = new Stopwatch(c, {delay: 456});
cTimer.start();
</pre>
<div class="stopwatch" id="c-timer"></div>456 ms<br>
<pre>
var d = document.getElementById("d-timer");
dTimer = new Stopwatch(d, {delay: 1000});
dTimer.start();
</pre>
<div class="stopwatch" id="d-timer"></div>1000 ms<br>
Get some basic HTML wrappers for it
<!-- create 3 stopwatches -->
<div class="stopwatch"></div>
<div class="stopwatch"></div>
<div class="stopwatch"></div>
Usage is dead simple from there
var elems = document.getElementsByClassName("stopwatch");
for (var i=0, len=elems.length; i<len; i++) {
new Stopwatch(elems[i]);
}
As a bonus, you get a programmable API for the timers as well. Here's a usage example
var elem = document.getElementById("my-stopwatch");
var timer = new Stopwatch(elem, {delay: 10});
// start the timer
timer.start();
// stop the timer
timer.stop();
// reset the timer
timer.reset();
jQuery plugin
As for the jQuery portion, once you have nice code composition as above, writing a jQuery plugin is easy mode
(function($) {
var Stopwatch = function(elem, options) {
// code from above...
};
$.fn.stopwatch = function(options) {
return this.each(function(idx, elem) {
new Stopwatch(elem, options);
});
};
})(jQuery);
jQuery plugin usage:
// all elements with class .stopwatch; default delay (1 ms)
$(".stopwatch").stopwatch();
// a specific element with id #my-stopwatch; custom delay (10 ms)
$("#my-stopwatch").stopwatch({delay: 10});
jsbin.com demo
