I have a bit of code, which refreshes my HTML page, everytime there is a new minute i.e. when seconds == 0.
<head>
<script>
function reload(){
location.reload();
}
function refresh(){
var d = new Date();
var s = d.getSeconds();
if (s == 0) {setTimeout(reload(), 1000)};
}
</script> </head>
<body onload="refresh(), setInterval('refresh()',1000)">
However, when it refreshes, it refreshes an infinite amount of times in the time that seconds == 0. I have tried to implement "setTimeout", in order to prevent this from happening - and so that it only refreshes once. However, this did not work and it is still refreshing an infinite amount of times while s == 0. Does anyone have any more ideas to prevent this from happening? Any questions, just ask. Thanks
If I understand correctly, you don't want to refresh after 1 minute from loading but refresh when second = 0.
You don't have to call refresh function constantly via interval.
We have current second. So, if we subtract from minute, we can find remaining seconds to new minute.
60 - d.getSeconds();
Then convert into milliseconds, set timeout, and page will be refresh exactly at new minute.
setTimeout(function() { location.reload() }, 1000 * (60 - d.getSeconds()));
If so important you can consider add/subtract milliseconds with d.getMilliseconds()
For JavaScript, you can simplify this down to:
setTimeout(() => {
window.location.reload(1);
}, 60 * 1000);
However a very simple solution not using JS is
<meta http-equiv="refresh" content="60; URL=https://example.com/">
In general the refreshin is not a nice way to do things. have you considered using asychronous calls and refreshing your DOM with JavaScript instead of reloading the whole page?
However if you want to pursue this route I'd take the current starting time as a base and check from here is 1 second has passed already.
const t0 = performance.now();
function refresh(){
if ((performance.now() - t0) >= 1000) {
location.reload();
}
}
However you'll need to call refresh untill this happens.
As for the "don't understand" comment, I cleand up a litle and I'll add some explanation here:
The first line is outside of all functions, so it sets a variable "globally", as it never changes I use a cosntant (instead of a variable) for speed and readability. It sets the current time in ms insode t0
const t0 = performance.now();
In your funcion I use the same command to get the ms again, and substract the formerly saved ms from it. If the new number is more than 1000 bigger than the original, a second has passed and it can do the reload.
if ((performance.now() - t0) >= 1000) {...
Related
I have an element #ChatStatus which is constantly changing, and when a change occurs, the element slides in being visible on screen.
What I'm trying to do now is: If there hasn't occurred any changes on this element for the last 5 seconds for example, hide the element back out of the screen. Here's my code:
$('#ChatStatus').on("DOMSubtreeModified",function(){
$('#ChatStatus').animate({'right':'30px'},500);
});
// Now I wanna run this, when the #ChatStatus is innactive, or no changes occurred
// $('#ChatStatus').animate({'right':'-200vw'},500);
Here's the full project where I want to implement this inactivity feature.
https://jsfiddle.net/shuffledPixels/77hb2do0/1/
Here is a very functional way of doing it. As your commenters have mentioned, this really isn't the best way of doing it; but if you want to, it's your code.
shouldRemove = null;
$('#ChatStatus').on("DOMSubtreeModified",function(){
clearTimeout(shouldRemove);
$(this).animate({'right':'30px'},500);
shouldRemove = setTimeout(function () {
$(this).animate({'right':'-200vw'},500);
}.bind(this), 5000);
});
I am not very experienced with JS animation and the like, so I'll leave any question of style and method choice up to you. Aside from that, I would suggest using a global variable holding the time of the last change, and polling at regular intervals to see if that time is more than 5 seconds ago. For example:
var lasttime = none
$('#ChatStatus').change(function () {
lasttime = new Date().getTime() //Set lasttime to the time when the element changed
}
setInterval(function () {
if ((new Date().getTime() - lasttime) > 5000) { //Date().getTime() is in miliseconds,
// so 5000 for five seconds
$('#ChatStatus').animate({'right':'-200vw'},500);
}
}, 1000); // Set 1000 (1 second) lower for more precision at the
// cost of more computational time
I hope this helps!
I'm trying to decrement a variable once a day. I have written the following code for that.
var counter = 10; //any value
setInterval(function() {
counter = counter - 1;
}, 86400000);
Is there a better or efficient way to achieve the same thing ?
P.S : - I do not wish to use any libraries.
The only thing I see you miss is to set the initial value of counter variable.
I would write:
var counter = 1000; // or any useful value
setInterval(function() {
--counter;
}, 24 * 60 * 60 * 1000); // this is more self-explanatory than 86400000, and, being evaluated just once, it will have a tiny effect on the performace of the script
I don't see any problem in the way you write it. You use interval, ok, but this is not the worst evil you may do to set up the variable value.
You may think of another solution with a function which returns you the current counter.
var initialValue = 20000;
function getCounter() {
return initialValue - Math.floor(Date.now() / 1000 / 60 / 60 / 24);
}
console.log(getCounter());
The difference is that it takes the current day number starting from the UNIX time beginning. Every day the day number will be increased, so the result of the function will be decreased by 1.
But still I don't see how this solution can be better than yours.
I'm not totally sure why, but using setInterval like this makes me uncomfortable.
If I were to require this, I would use something like this approach:
var counter = 10;
var timeout = new Date();
setInterval(function(){
if(new Date() >= timeout)
{
--counter; // the action to perform
timeout = new Date(timeout.getTime() + 86400000); // update the timeout to the next time you want the action performed
}
console.log(counter);
},1000); // every second is probably way more frequent than necessary for this scenario but I think is a decent default in general
One thing that this allows is to, for example, set the next timeout to midnight of tomorrow rather than being locked in to "X seconds since the previous execution". The key is the inversion of control - the action itself can now dictate when it should next run.
Though I would probably abstract away the details behind an interface accepting a start, interval, and action.
The biggest problem in my eyes is that you have to keep this one JS process running consistently for days at a time to have it do what you need. The world is not so perfect that things don't need an occasional reboot...including the average JS process.
Personally I would store a timestamp of my starting point, then (whenever I need to know how much time has elapsed) grab a new timestamp and use it to calculate how many days it has been. That way even if something interrupts my process I can still be right where I started.
Maybe use window.localStorage to save the last time, and if it is greater than 60*60*24 (seconds in a day) set the last time to this morning/now/1:00 and then decrease the value and save it.
Example:
var d = new Date();
var mins = -(1+d.getHours())*60+d.getMinutes();
var secs = mins*60+d.getSeconds(); // total seconds passed today from 1:00
var now = d.getCurrentTime():
var lastCheck = localStorage.getItem("lastCheck");
if (!lastCheck)
{
localStorage.saveItem("lastCheck",now-secs); // beginning of today
}
var dayPassed = now - lastCheck > 24*60*60; // change to see if a day has passed
if (dayPassed)
{
// save seconds
localStorage.setItem("counter",localStorage.getItem("counter")-1);
localStorage.saveItem("lastCheck",now-secs); // beginning of today
}
It makes more sense to me to check how many days have passed since a specific date and decrement that number of days from the counter. Mostly just because I wouldn't expect anybody to leave the same page open without the need or want to reload for days on end. I would do something like this:
counter = 365; // original counter
var start = new Date(2016, 03, 20); // original date
var now = new Date();
var days = Math.floor(Math.abs(start.getTime()-now.getTime())/(24*60*60*1000))
counter -= days;
That way every time you visited the page, it would be decremented correctly. Note that this ignores any issues with leap days or time zones. The example above would have a counter of 360 for me. And then if you did expect it to be open for days, reload it automatically with:
self.setTimeout(function(){document.location.reload()}, 86400000);
What's the best way to create a timer in JS?
I've been using this so far:
var sec = 0;
setInterval(function (){sec +=1}, 1000);
I've noticed that, when I need miliseconds, it slows down by a lot. On browser tab changes, it completely stops.
var milisec = 0;
setInterval(function (){milisec +=1}, 1);
I'm looking for a better way to handle this, which will also continue to work when the browser window is changed.
With milliseconds, the resolution of the timer isn't large enough. In most cases the callback won't be called more often than roughly 50 to 250 times per second, even when you set the interval to 1ms. See Timer resolution in browsers (as referred to by Sani Huttunen) for an explanation.
With 1000ms it will work better. But still the timer won't be fired when the tab is inactive, and may be delayed when the cpu is busy or another script is running on your page.
One solution is to not increment a counter, but to test how much time has actually passed since the previous call of the timer. That way, the timing remains accurate, even when the intervals have been delayed or paused inbetween.
This snippet will remember the start date, and on each timer interval, update seconds and milliseconds to the difference between the current time and the start time.
var start = new Date();
var milliseconds = 0;
var seconds = 0;
setInterval(function()
{
var now = new Date();
milliseconds = now.getTime() - start.getTime();
seconds = round(milliseconds / 1000);
}, 1000);
I've set the interval to 1000 again. You might set it shorter, but it will cost more performance.
Related question: How can I make setInterval also work when a tab is inactive in Chrome?
Based on #goleztrol's solution, I've created an alternate solution specifically for my situation (it might not work for everyone).
I just ask the exact time when it's needed with this function, to know the exact miliseconds passed:
var start = new Date();
var msPassed = function() {
var now = new Date();
var ms = now.getTime() - start.getTime();
return ms
}
msPassed(); //returns time passed in ms
I needed to position objects (on creation) depending on how much time passed until their creation, so for my case this is a perfect solution. However, my initial question asks for the perfect timer, and this is not it. Anyway, here it is for future reference.
The code I wrote to call a function on the minute every minute, I think is flawed, as It's good for a while, but tends to lag behind by about 15 seconds for every hour since the page was loaded. To be honest I can't figure out what's causing the lagging, maybe it's the time it takes the functions to execute, small lapses all adding up and accumulating. Is there a way to auto-correct the lapses within the function as it's called. Or maybe someone knows a better method of achieving on the minute function calls. Any help or ideas much appreciated. Thanks.
var now = new Date();
var delay = 60 * 1000; // 1 min in msec
var start = delay - (now.getSeconds()) * 1000 + now.getMilliseconds();
setTimeout(function setTimer() {
onTheMinFunc();
setTimeout(setTimer, delay);
}, start);
First of all, the DOM Timers API does not guarantee accuracy. I quote:
This API does not guarantee that timers will run exactly on schedule. Delays due to CPU load, other tasks, etc, are to be expected.
Second, you have a lag on each round caused by the time onTheMinFunc() is executed (you only set the timeout when it's done).
So, let's say onTheMinFunc takes half a second to execute - you get half a second delay at each minute and it accumulates - after only 10 minutes it'll lag quite a bit. (Note, functions should usually not take more than 15ms to execute anyway to avoid noticeable lag)
Try:
setInterval(onTheMinFunc, delay);
It still won't be very accurate. You can poll on much shorter intervals and keep track of a date variable - but again - no guarantees.
What you probably want is setInterval:
setInterval(onTheMinFunc, delay);
As is, your code using setTimeout means that the time it takes to execute your onTheMinFunc is being added into your delay before the next one is started, so over time, this extra delay will add up.
Using setInterval will be more accurate, since the delay is between calls to execute the function, rather than starting the timer only after the function is finished.
Timers and javascript times aren't very accurate, and I would think the only way to make sure a function is executed every whole minute over time, is to check the seconds every second
setInterval(function() {
if ( new Date().getSeconds() === 0 ) onTheMinFunc();
},1000);
FIDDLE
Here is a slight modification to your code:
function everyMinute(fn) {
arguments[1] && fn();
var now = new Date();
var delay = 60 * 1000 - (now.getSeconds()) * 1000 + now.getMilliseconds();
setTimeout(function(){
everyMinute(fn, true);
}, start);
}
everyMinute(onTheMinFunc);
It recalculates the number of milliseconds to wait till the next minute every time so it is as accurate as possible to the top of the minute.
I think you want something closer to this:
function setNextMinute() {
// figure out how much time remains before the end of the current minute
var d = new Date().getTime()%60000;
//set a timeout to occur when that expires.
setTimeout(function () {
// recalculate a new timeout so that your timer doesn't lag over time.
doWhateverYouWantToHere();
// note that calling doWhateverYouWantToHere() will
// not offset the next minute, since it is recalculated in setNextMinute()
setNextMinute();
},60000-d);
}
setNextMinute();
caveat: I did not thoroughly test this for timing. But it appeared to work for 1 sec intervals and 1 min intervals well enough.
This has the advantage of not recalculating every second, and also not just starting a 60 second timer from whatever the current time is.
The current accepted answer may overkill
Executing if ( new Date().getSeconds() === 0 ) onTheMinFunc(); on each second (and forever) seems to not be a good idea.
I will not benchmark it against the following propositions, it's not necessary.
Clues
Use whatever logic is necessary to calculate the start moment.
On the start moment
Use setInterval for remaning executions
Execute the first call
Note setInterval is called ASAP to avoid that time lapses.
If you want that new Date().getSeconds() === 0:
var id = setInterval(function() {
if ( new Date().getSeconds() === 0 ) {
setInterval(onTheMinFunc, delay);
onTheMinFunc();
clearInterval(id);
}
},1000);
Alternatively, you could use your own logic:
var now = new Date();
var delay = 60 * 1000; // 1 min in msec
var start = delay - (now.getSeconds()) * 1000 + now.getMilliseconds();
setTimeout(function() {
setInterval(onTheMinFunc, delay);
onTheMinFunc();
}, start);
Please check both examples working on jsfiddle
The second (Example B) seems more accurate.
I'm trying to make a countdown that is counting down in milliseconds; however, the countdown actually takes much longer than 7 seconds. Any idea as to why?
function countDown(time){
var i = 0;
var interval = setInterval(function(){
i++;
if(i > time){
clearInterval(interval);
}else{
//mining
$('#mining_time').text($('#mining_time').text()-1);
}
}, 1);
}
And I can confirm the varible time passed to the function is correctly set to 7000.
For a mostly-accurate countdown, use setTimeout().
setTimeout(fn, 7e3);
If you absolutely must have it as close to 7 seconds as possible, use a tight poll (requestAnimationFrame()) and look at difference between the time of start and current poll.
var startTime = Date.now();
requestAnimationFrame(function me() {
var deltaTime = Date.now() - startTime;
if (deltaTime >= 7e3) {
fn();
} else {
requestAnimationFrame(me);
}
});
Poly-fill as required.
the most precise way to run something after 7 seconds - is to use setTimeout with 7000 ms interval
a. there is no browser that guarantees an interval to run with 1ms resolution. In the best case it would be 7-10ms
b. there is only one thread in js, so the tasks are queued. It means that the next run will be scheduled to only after the current run is finished.
Some useful reading: http://ejohn.org/blog/how-javascript-timers-work/
No browser will take 1 as parameter for setInterval. Off the top of my head the minimum is 4 ms.
For an accurate result, get the current time, add 7000 ms, and poll (using setInterval or setTimeout) until you reach that new time.
A quick Web search returned this article that provides an example.
[Update] the value of 4 ms is mentioned on this MDN page.