Note: I just found out this doesn’t work in Internet Explorer. If you happen to use Internet Explorer I’m sorry; I’m sorry that you haven’t been shown a better browser sooner. Get Firefox.

In continuing my CS162 project I decided my previous timer wasn’t all that pimp since I needed to add a few attributes such as a pause/stop method and a reset method. Using the previous single function method somewhat worked for this but the number of arguments that needed to be passed to the function grew rather quickly, and in addition I had to make use of global variables. It was at this point I knew I needed to move the timer into a class to make it more portable and thus I came up with BTimer.

The BTimer Class allows one to run multiple Javascript timers without having to worry about the details of the setTimeout function or setInterval. This is particularly useful in cases where a page has different AJAX portions that need to be updated at different rates.

// Bryce Boe
function BTimer(interval,f,args) {
BTimer.prototype = {
    init:function(interval,f,args) {
        this.running = false; = interval;
        this.count = 0;
        this.limit = Infinity;
    _run:function() {
        if (!this.running) return;
        if (this.count>=this.limit) {
        var self=this;
    start:function() {
        if (!this.running) {
            this.running = true;
            if (this.startFunc != null)
    stop:function() {
        if (this.running) {
            this.running = false;
            if (this.stopFunc != null) this.stopFunc.apply(null,this.stopArgs);
    reset:function() {
        this.count = 0;
        if (this.resetFunc != null) this.resetFunc.apply(null,this.resetArgs);
    setUpdateFunction:function(f,args) {
        this.updateFunc = f;
        this.updateArgs = args;
    setStartFunction:function(f,args) {
        this.startFunc = f;
        this.startArgs = args;
    setStopFunction:function(f,args) {
        this.stopFunc = f;
        this.stopArgs = args;
    setResetFunction:function(f,args) {
        this.resetFunc = f;
        this.resetArgs = args;
    setLimit:function(limit) {
    setInterval:function(interval) {;
    getCount:function() {
        return this.count;

The init function is the constructor for the BTimer class and called automatically when one writes: “new BTimer(someFunc,someList)”. The constructor takes as its first argument the update interval in milliseconds, the name of the function to call on update and finally a list of arguments that should be passed to the update function. If the update function takes no arguments one must simply pass in an empty array [].

The BTimer’s _run() function is where the magic occurs and should never be called directly. This function verifies that it should be running and if so it increments the count, calls the update function, and then creates the timer loop. In the event we reached the run limit it calls its stop function so that the optional user defined stop function may be called.

The BTimer’s start() function calls the optional user specified start function, and then begins the timer by calling _run(). It also checks to see if it has already been started so that it doesn’t initialize a parallel setTimeout command.

The BTimer’s stop() function stops the timer and calls the optional user specified stop Function. The stop function acts like a tape player rather than a cd player as on resume (calling start()) the counter continues where it left off.

The BTimer’s reset() function resets the count back to zero and optionally calls the user defined reset function. Note that this does not change the running status of the counter.

The setUpdateFunction, setStartFunction, setStopFunction and setResetFunction all set their respective optional functions. Each take the function to be called on the particular event and the arguments that should be passed to that function as a list. Just like the constructor if the function takes no arguments then an empty array [] needs to be passed in as the second argument.

The setLimit function updates the timer limit. By default the timer limit is the javascript value Infinity.

The setInterval function updates the wait time between the update function calls. This can be called while the timer is running and will take place after the event from the last setTimeout function occurs. An example to demonstrate this is calling start on a one minute timer and then immediately changing the interval to be 5 seconds. The 5 second interval wont take place until the one minute timer has expired.

Finally the getCount() function returns the timer count.

To demonstrate BTimer in action check out the following:

Count: 0

0.3 second 1 second 5 seconds

Note: Clicking on reset does not update the count to 0.

The extra needed javascript functions for this are the following:

function BTimerMyStart0() {
    if (typeof BTimerMyTimer0 == 'undefined') {
        BTimerMyTimer0 = new BTimer(300,BTimerMyUpdate0,[]);
        BTimerMyTimer0.setResetFunction(BTimerOther0,['called reset']);
        BTimerMyTimer0.setStartFunction(BTimerOther0,['called start']);
function BTimerMyUpdate0() {
    document.getElementById('BTimerDynamic0').innerHTML="Count: "
function BTimerMyPause0() {
    BTimerOther0('called pause');
function BTimerOther0(string) {
    if (typeof BTimerMyStatusCount0 == 'undefined') BTimerMyStatusCount0 = 0;
    document.getElementById('BTimerStatus0').innerHTML = BTimerMyStatusCount0++
        +": " + string + "\n"
        + document.getElementById('BTimerStatus0').innerHTML;

And the accompanying html:

<textarea id="BTimerStatus0" style="width:200px;height:150px;">Status Area</textarea>
<div id="BTimerDynamic0">Count: 0</div>
<input type="button" value="Start" id="BTimerStart0" onclick="BTimerMyStart0();" />
<input type="button" value="Pause" id="BTimerPause0"
       onclick="BTimerMyTimer0.stop();" DISABLED />
<input type="button" value="Reset" id="BTimerReset0"
       onclick="BTimerMyTimer0.reset();" DISABLED />
<input type="radio" id="BTimerRadio00" name="BTimertimeout"
       BTimerOther0('selected .3 second');" CHECKED DISABLED/> 0.3 second<br/>
<input type="radio" id="BTimerRadio10" name="BTimertimeout"
       BTimerOther0('selected 1 second');" DISABLED/> 1 second<br/>
<input type="radio" id="BTimerRadio20" name="BTimertimeout"
       BTimerOther0('selected 5 seconds');" DISABLED/> 5 seconds<br/>

This javascript code is fairly self explanatory with the exception of BTimerMyStart0. Since I want to create my timer the first time I call start it is necessary to verify that upon further start button presses the same does not occur. This is what line 8 does. One can also see that I set the limit to 50 in addition to setting start, stop and reset functions. Just a reminder that these functions are purely optional; I’m using them to demonstrate their purpose.

Once the start function is called we now have a variable BTimerMyTimer0 which points to our timer object. We interact with this object by defining our onclick actions with the pause and reset buttons.

Finally the BTimerOther0 function simply updates the textarea with the string it receives. This function demonstrates passing arguments to a user defined event function.

Well I think that’s it, feel free to use BTimer.js but please keep the two lines of comments so that one may have access to this post for support on the timer.

BTimer Class Source


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