Develop Reference

Timer using frameRate and frame counter reliable?

I'm using p5js to program an animation with a timer countdown. I set my timer up to be updated each frame within an object that is being animated by the draw() function in sketch. Because of this, setInterval() will not work for what I'm trying to do.
I thought I could use the frameRate and a frame counter to decide if a second has passed:
this.updateTimer = function(){
this.framecounter++;
if(this.framecounter > frameRate()){
this.framecounter = 0;
//increment seconds
}
}
Is this reliable? I tested it against an actual timer and it seems to be about 1 second ahead after about 15 seconds. Is there a better way to do this by calling a function each frame? Thanks!

Why don't you just use the frameCount variable? More info is available in the reference.
You could also use the millis() function instead. Again, the reference is your best friend.
If you still can't get it working, please post a MCVE (or better yet, a CodePen or JSFiddle) that we can run to see the problem.

CodeHS JavaScript Timer- Countdown

I work on CodeHS and need to make a countdown timer for my powerups in the game I'm making, Breakout. I need the timer to be reusable so no for loops, it needs to go down in seconds/milliseconds (it doesn't matter which) and preferably last 30 seconds or 30,000 milliseconds. Remember this is CodeHS I'm working on.

If you want something to happen 30 seconds after you start your timer you could do something like this:
//set the time remaining to 30 outside of a function so it is global
var timeRemaining = 30;
function start(){
//set the timer to run the function countdown once every second(1000 milliseconds)
setTimer(countdown, 1000)
}
function countdown(){
/*every time it is called this function subtracts one from the time if it is
more than 30, when it reaches 0 stops the timer and resets the time*/
if(timeRemaining<=0){
stopTimer(countdown);
timeRemaining = 30;
println("Done");
//30 seconds has passed, do what you need here(call your function)
}else{
timeRemaining--;
println(timeRemaining+" seconds left")
}
}
Add your function or whatever you want to happen after the time is up whereprintln("Done") is.
Because timeRemaining is set back to 30 at the end, you can reuse the timer by calling setTimer(countdown, 1000) again.
You can remove the println statments, they are just to see what is happening.
If CodeHS doesn't want hardcoded numbers (I think they call them "magic numbers"), replace the 30s with a constant set to 30.
Let me know if you need a better explanation.

Tell me if I'm wrong because I have no idea what CodeHS is, but I am quite sure that this can be achieved with a simple setInterval function.
To go by full seconds:
var timer=30;
setInterval(function(){
timer-=1;
document.getElementById(timerId). innerHTML=timer;//shows the remaining time
}, 1000);//subtracts 1 second from timer each second
To go by tenths of a second
var timer=30.0;
setInterval(function(){
timer-=0.1;
document.getElementById(timerId). innerHTML=timer;//shows the remaining time
}, 1000);//subtracts a tenth second from timer every 0.1 seconds

var timeLeft = 60;
var txt = new Text(" ","30pt Arial");
function start(){txt.setPosition(200,200); txt.setColor(Color.black); add(txt); setTimer(countdown,1000);}
function countdown(){drawTimer(); timeLeft--;}
function drawTimer(){txt.setText(timeLeft);}

Javascript increasing a value and the velocity on increasing it

I need to increase a number and I used setInterval(Function, time)
so I put a variable for time: time = 1000 now I need to change it so I put a function that changes it when I click a button:
function changetime() {time = time - 100;}
but it seems that you can't change the time of setInterval while is working...
how can I do that?
I tried with a setTimeout but the number now changes "jumping". is not regular...
I'm not sure but it seems that the "jump" changes when I change the setTimeout time... like if the timeout is now in the setInterval time.
Original code---_>
var time = 1000;
function interval() { setInterval(Function, time);}
function changetime() {setTimeout(interval, 10);tempo = tempo - 200;}

I had the same problem some time ago, and i made a small function that can do this:
https://github.com/Atticweb/smart-interval/blob/master/smart-interval.js
It works like this:
var timer = new timer();
timer.start(function(){
//more magic here
}, 3000, true);
//change the interval
timer.set_interval(4000);
I hope this helps you, good luck!

How to trace in the console how many intervals are being executed - JavaScript

I have a problem trying to know if a setInterval() is taking place or it was killed.
I am creating an interval and saving it into a variable:
interval = setInterval('rotate()',3000);
Then on click to an element I stop the interval and wait 10 seconds before starting a new one, by the way the variable interval is global:
$(elm).click(function(){
clearInterval(interval);
position = index;
$('#banner div').animate({
'margin-left':position*(-img_width)
});
setTimeout('startItnerval()',10000);
});
function startItnerval(){
interval = setInterval('rotate()',3000);
}
It seems to work but eventually I can realize that there are intervals still being in place, everytime I start a new interval it is saved in the interval variable, which is global, so in theory even if I start 100 intervals they are all saved in the same variable replacing the previous interval right? So I should only have one instance of interval; then on clearInterval(interval); it should stop any instance.
After looking at the results, apparently even if it is saved in the same variable, they are all separate instances and need to be killed individually.
How can I trace how many intervals are being executed, and if possible identify them one by one? even if I am able to solve the problem I really would like to know if there is a way to count or show in the console how many intervals are being executed?
thanks

jsFiddle Demo
As pointed out in comments, the id's constantly increase as timers are added to a page. As a result, it may be possible to clear all timers running on a page like this:
function clearTimers(){
var t = window.setTimeout(function(){
var idMax = t;
for( var i = 0; i < idMax; i++ ){
window.clearInterval(i);
window.clearTimeout(i);
}
},4);
}
The reason that you can only see one interval is because every time you start a new interval, you overwrite the value in interval. This causes the previous intervals to be lost but still active.
A suggestion would be to just control access to your variable. Clearly there is an issue where the start function is called too often
clearInterval(interval);//when you clear it, null it
interval = null;
and then take advantage of that later
if( interval != null ){
interval = setInterval('rotate()',3000);
}
Also, as Pointy noted in a comment, using a string to call a function is not best practice. What it basically does is converts it into a Function expression which is similar to using eval. You should probably either use the function name as a callback
setInterval(rotate,3000);
or have an anonymous function issue the callback
setInterval(function(){ rotate(); },3000);

setInterval returns an Id, not the actual object, so no, no interval will be overriden if you repeat the line
var xy = setInterval(function() {...}, 1000);
If you want to stop the interval you have to clear it:
clearInterval(xy);
And if your startInterval can be called multiple times in a row, but you don't want to create multiple intervals, just clear the inverval before you start a new one:
function startInterval(){
clearInterval(interval);
interval = setInterval('rotate()',3000);
}
If you have to create multiple intervals, you could save the ids in an array to keep track of them:
var arr = [];
//set the interval
arr.push(setInterval(...));
//get number of currently running intervals
var count = arr.length //gives you the number of currently running intervals
//clear the interval with index i
clearInterval(arr[i]);
arr.splice(i, 1);

Counting down for x to 0 in Javascript?

I have from the backend a time on the format 00:12:54 and I display it to the screen. But, I would like to have this time to continue to go down. I have though to create a variable in javascript that will old the time and with setTimeout to loop to display with document.getElementById the new value. I think it can be problematic if I have many time to go down in same time. I might require an array?
How would you do that? If I have no other suggestion, I will try my way, but I am curious to know if it does have a more secure way to do it.

Do you know jQuery Framework? It's a Javascript framework that have a lot of utilities methods and functions that let you do Javascript stuff more easily.
Here is a count down plugin (haven't tested it).
I suggest you to download JQuery than download the plugin . Check the sample of code from the "relative" tab on the website. You can have something like :
$('#until2d4h').countdown({until: '+12M +54S'});
*The only drawback with what I suggest you is that you will require 2 .js to be added. Try to add them only when needed and you will be find.

General algorithm:
Read time from server.
Read the current time.
Call a function.
In your function, read the current time, get the delta from the initial time you read in step 2.
Subtract the delta from the initial time you read from the server in step 1 and display the remainder.
The function should call window.setTimeout to call itself in 1000ms (or adjust according to time elapsed within the function), if you want to continue counting down.
Here's a rough cut:
window.onload = function () {
var countdown_start_in_ms = 6000; // from server
function tick() {
var now = new Date().getTime();
var disp = start - now;
if (disp < 0) {
disp = 0;
}
var el = document.getElementById("countdown");
el.innerHTML =
// quick hack to format time
/(\d\d:\d\d:\d\d) ...$/.exec(new Date(disp).toUTCString())[1];
if (disp > 1000) {
var elapsed = new Date().getTime() - now;
window.setTimeout(tick, 1000 - elapsed);
} else {
// stop countdown and set color to light grey
el.style.color = "#ccc";
}
}
var start = new Date().getTime() + countdown_start_in_ms;
tick();
}

You won't like the taste of this one, but it'll do you good:
Google for 'javascript timer' and get your hands dirty reading through the various examples and tutorials returned by that search.
You'll learn a lot more than just how to write a count-down timer. :-)
Good luck!

Take a look at Grab hands and set your own time. and inspect its code. While it is written with Dojo, the "clock" part is in plain JavaScript. In your case the only difference is how to advance the counter — decrease rather than increase it.