Best way to have an event happen n times?
I am using the following code to create countdowns in Javascript. n is the number of repetitions, frequency is the number of milliseconds to wait before executing, funN is the function to call each iteration (usually a function that updates a portion of the DOM), and funDone is the function to call when the countdown is complete.
function timer(n, freq, funN, funDone)
{
if(n == 0){
funDone();
}else{
setTimeout(function(){funN(n-1); timer(n-1, freq, funN, funDone);}, freq);
}
}
It can be called like this:
timer(10,
1000, /* 1 second */
function(n){console.log("(A) Counting: "+n);},
function() {console.log("(A) Done!");}
);
timer(10,
500,
function(n){console.log("(B) Counting: "+n);},
function() {console.log("(B) Done!");}
);
The advantage of this is that I can call timer () as many times as I want without worrying about globals etc. Is there a better way to do this? Is there a clean way to make setInterval stop after a certain number of calls (without using globals)? This code also creates a new lambda function every time setTimeout is called, which seems to be problematic for large countdowns (I'm not sure how the javascript garbage handler does this).
Is there a better way to do this? Thank.
source to share
I would create an object that receives a counter and receives a function pointer, something similar to the following pseudo code:
TimedIteration = function(interval, iterations, methodToRun, completedMethod){
var counter = iterations;
var timerElapsed = methodToRun; //Link to timedMethod() method
var completed = callbackMethod;
onTimerElapsed = function(){
if (timerElapsed != null)
timerElapsed();
}
onComplete = function(){
if (completed != null)
completed();
}
timedMethod = function(){
if (counter != null)
if (counter > 0) {
setTimeOut(interval, onTimerElapsed);
counter--;
}
else
onComplete();
this = null;
}
}
if ((counter != null)&&(counter > 0)){
//Trip the initial iteration...
setTimeOut(interval, timedMethod);
counter--;
}
}
obviously this is pseudo code, I haven't tested it in the IDE and syntactically not sure if it will work like [I would be surprised if there is] but basically what you do you create a wrapper object that receives time interval, number of iterations, and method to start on expired timer.
Then you call this in your method to run like this:
function myMethod(){
doSomething();
}
function doWhenComplete(){
doSomethingElse();
}
new TimedIteration(1000, 10, myMethod, doWhenComplete);
source to share
This is basically the same idea as @balabaster, but it's tested, uses a prototype, and has a slightly more flexible interface.
var CountDownTimer = function(callback,n,interval) {
this.initialize(callback,n,interval);
}
CountDownTimer.prototype = {
_times : 0,
_interval: 1000,
_callback: null,
constructor: CountDownTimer,
initialize: function(callback,n,interval) {
this._callback = callback;
this.setTimes(n);
this.setInterval(interval);
},
setTimes: function(n) {
if (n)
this._times = n
else
this._times = 0;
},
setInterval: function(interval) {
if (interval)
this._interval = interval
else
this._interval = 1000;
},
start: function() {
this._handleExpiration(this,this._times);
},
_handleExpiration: function(timer,counter) {
if (counter > 0) {
if (timer._callback) timer._callback(counter);
setTimeout( function() {
timer._handleExpiration(timer,counter-1);
},
timer._interval
);
}
}
};
var timer = new CountDownTimer(function(i) { alert(i); },10);
...
<input type='button' value='Start Timer' onclick='timer.start();' />
source to share
I like your original solution better than the alternatives suggested, so I just changed it so as not to create a new function for each iteration (and the argument fun()
now has a value before decrementing - change if necessary ...)
function timer(n, delay, fun, callback) {
setTimeout(
function() {
fun(n);
if(n-- > 0) setTimeout(arguments.callee, delay);
else if(callback) callback();
},
delay);
}
source to share