I need to invoke some function given number of times through given delays. How should I do - declare variable for timer and pass it to invoking function for stopping timer in some moment or in loop (n times) invoke setTimeout once ( or some another approach to skeep delay time once) or other.Thanks.
edit to fix syntax eror
var timerID = null;
var n = 5;
this.timerID = setInterval(function(){
funcToInvoke(n,timerID){
if(invokeNumber == n){
clearInterval(timerID);
return;
}
else { do something}
}
},delay)
Yes, the approach is common and better than calling setTimeout in a loop (with a fixed number of times). It is more performant than that and also more flexible, because the interval will be stopped dynamically (might check for a future condition).
However, your code is a bit messy. Fixed:
// Assuming we a have
// n
// delay
// funcToInvoke
// and execute in context of some object
var that = this,
numberOfInvokes = 0;
this.timer = setInterval(function() {
// "this" points to the global object
if (numberOfInvokes == n)
clearInterval(that.timer);
else
funcToInvoke(numberOfInvokes);
numberOfInvokes++;
}, delay);
Your current method has a syntax problem, you can't have a function parameter like this.timerID). In fact, you should remove the whole funcToInvoke declaration, and declare n and timerID as local variables, so they will be available to the closure. Like this:
// Don't forget to define n here!
var n = 5;
// Change timerID to local var instead of property
var timerID = null;
timerID = setInterval(function(){
if(invokeNumber == n){
clearInterval(timerID);
return;
} else {
//do something
}
// You can setTimeout again anywhere in this function if needed
}, delay);
If you want an approximate delay, setInterval is probably ok. If you want a more precise interval, then repeated calls to setTimeout are better as you can adjust the length of time to the next call based on the time since the last call.
E.g. for a clock ticking every second, you can do repeated calls to setTimeout, setting the lag to just after the next full second.
Related
So from what I have understood, setInterval() is used to call a function on repeat on regular intervals.
So basically it is a loop that executes a function forever periodically.
I am confused as to if I had to stop this execution at one point what would be the way to do it
for eg I am trying to print the message "hey" 3 times after 1 second each, but somehow it is printing it 3 times every second and is going on forever.
What can I do to stop it after a set number of times.
This is the code that I've been trying
var i = 3;
function message() {
console.log("hey");
}
while(i > 0) {
setInterval(message, 1000);
i = i - 1;
}
Your code is executing the setInterval thrice in the while loop, which is not needed.
Actually, setInterval does not work as a function call but actually registers a function to be called at some interval.
The setInterval() method will continue calling the function until clearInterval() i.e it is deregistered or the process is killed.
It should work like this
var i = 3;
var interval = setInterval(message, 1000);
function message() {
if (i === 0) {
clearInterval(interval);
}
console.log("hey");
i = i - 1;
}
To clear a setInterval, use global clearInterval method.
Example:
var timerId = setInterval(func, 500);
.... some code here....
clearInterval(timerId);
What can I do to stop it after a set number of times.
usually you don't use setInterval() for this, you use setTimeout().
Something like
var counter = 0;
function message() {
console.log("hey");
// we trigger the function again after a second, if not already done 3 times
if (counter < 3) {
setTimeout(message, 1000);
}
counter++;
}
// initial startup after a second, could be faster too
setTimeout(message, 1000);
The setInterval function calls the function indefinitely, whereas setTimeout calls the function once only.
Simply use clearInterval once the count runs out.
var i = 3;
function message(){
console.log("hey");
if (--i < 0) {
clearInterval(tmr);
}
}
var tmr = setInterval(message, 1000);
you have to assign that setInterval to a javascript variable to name it what for this setInterval, like this
var messageLog = setInterval(message, 1000);
After, in setInterval message function add this condition to clear the inverval whenever you want to clear.
function message(){
if(i>3) {
clearInterval(messageLog); // clearInterval is a javascript function to clear Intervals.
return null;
}
console.log("hey");
}
You can retrieve the timer when creating and clear it if needed.
var i=3;
var timer = setInterval(message,1000);
function message(){
console.log("hey");
i—-;
if(i==0)
clearInterval(timer)
}
a beginner here too,look for clearInterval method ...
I have a function called "showCustomer" that get number between 1-5 and return something.
I want to use setInterval, to run this function every 5 second but with another number.
Its not working, i don't understand why its not working to me. here is the code.
setInterval(function () {
var i = 1;
showCustomer(i);
i++;
}, 5000);
Just move the declaration of variable i before the setInterval() call:
var i = 1;
setInterval(function () {
showCustomer(i);
i++;
}, 5000);
The anonymous function you've set as a callback for setInterval gets called every 5 seconds in your code. In every call, you're setting i to 1 which resets it every time.
Moving i outside the setInterval callback makes it persist the the current value.
Every time you use var, you redeclare the value of that variable. So you only should declare the counter one time.
Every time that the browser calls the callback showCustomer the if statement evaluates if the browser should make a new call.
clearInvertal() it's the method to stop the setInterval() method.
var id = 1;
var show5times = window.setInterval(showCustomer, 5000);
function showCustomer() {
alert(id);
id++;
if(id > 5) {
window.clearInterval(show5times);
}
}
I am trying to make a function(next) that takes a function and a wait time as its arguments. It will then have a counter that will be increased by the function calls.
var up = function() {
var counter = 0;
return counter += 1;
};
var next = function(fn, wait) {
var total = 0; //set total variable to 0
var x = fn(); //call the function and set answer to a variable
total+=x; //add the answer to the total
var n = setTimeout(function(){fn();}, wait);
//THIS BIT DOES NOT GIVE ME 1? Instead I get any number from 16 (depenging on how many times I call it! It increases as I keep calling the function....?!)
total += n;
return total;
};
next(up,1000);
I am totally confused as to why setTimeout is working like this?!
I have looked around for an answer for this and have not hit lucky- I am sorry if I have missed the question on here if it has been asked before!
I did come across this question and tried putting the variable counter outside, however this did not seem to make any difference...
This question seems even closer to the area I am confused about however I am not any closer to comprehending my problem any help would be greatly appreciated as to why the return values that I am getting are so much higher than what I expect them to be..
Another approach that I tried was this:
var next = function(func, wait) {
var storedAnswer = 0;
var answer = function() {
return storedAnswer;
}
var increase = func;
setTimeout(increase, wait);
return answer();
};
next(up, 100); // gives me 0...? the up function here is defined in the above code...
But this ended up with me not getting any movement in the answer...
setTimeout returns the timeout id, not the return value of the callback.
var timeoutID = window.setTimeout(code, [delay]);
Try this:
setTimeout(function(){total += fn();}, wait);
The value that setTimeout returns is an int. But it is also a global counter of timeouts. Which is to say that every timeout shares the same counter. So that you get 16 just means that somewhere, in some part of your page, 15 other timeouts had already executed.
This is perfectly normal to get back an integer of 16 or basically of not 1 in that scenario, and using that integer with a clearTimeout for example will still properly reference the timeout used.
Aside
In node.js (which doesn't seem like what you are using), the mechanism is the same, except that a timeoutObject is returned instead which may still be used to clear the timeout. It is also used for continuations and other server-side related timing mechanisms.
n is the return value of setTimeout, which is a numeric identifier that you can pass to clearTimeout in order to cancel the timeout.
Your basic problem here is that setTimeout simply registers a function to be called after the given delay, and then execution immediately continues to the next line. So this line:
total += n;
is not waiting until your timeout completes. It's happening immediately, and n is, like I said, not the value you want.
You need your next function to take a callback that it can call when the timeout has completed.
var next = function(fn, wait, callback) {
var total = 0;
var x = fn();
total+=x;
setTimeout(function() {
var n = fn();
total += n;
callback(total);
}, wait);
};
You would call it like:
next(up, 100, function(total) {
// This function runs after the operation is done; do something with the total.
});
I have a function in JavaScript. I use setInterval in order to control my function. I also have another logic for controlling my function. I have a counter which is increased once one condition happens and is decreased when another condition happens. Now, sometimes the second condition does not happen and hence my function won't be resume anymore. (I pause my function when my first condition happen). Therefore, I want to wait at most 30 seconds for the second condition. If it does not happen, then I want to resume my function anyway. I have following code, but it does not work as I expect it. What happens is that it resume my function every 30 seconds. Then, it may be resumed while it should wait. Can someone let me know what is the problem with my code?
Please note that, the value for the counter may increase to more than 20. I mean the first and second condition may occur more than once.
function main()
{
// body
}
function increaseCounter()
{
counter += 1;
clearInterval(controller);
controlSecond = setInterval(function(){
counterSeconds += 1;
if (counterSeconds == 30)
{
counterSeconds = 0;
controller = setInterval(main, 100);
clearInterval(controlSecond);
}
}, 1000);
}
function decreaseCounter()
{
counter -= 1;
if (counter == 0)
{
counterSeconds = 0;
clearInterval(controlSecond);
controller = setInterval(main, 100);
}
}
Consider what happens if you call increaseCounter twice in a row.
On the first execution it will create interval A and assign it to controlSecond.
On the second execution it will create interval B and assign it to controlSecond, while interval A continues to fire off indefinitely. You won't stop it with clearInterval(controlSecond) because controlSecond no longer references interval A.
The problem is that you continue to set controlSecond and controller to a new interval without clearing them first. That results in the intervals being leaked with no way of clearing them. It's sort of like a memory leak where you have dynamically allocated memory but nothing pointed at it, but instead of renegade memory you have renegade intervals.
One way to prevent this is to make sure you always clear your interval before setting it.
I would also recommend that you implement controlSecond with a setTimeout because that is designed for tasks which only happen once.
Why not
var counter = 0
var timeout = null
function main () {
clearTimeout(timeout);
timeout = null;
}
function increaseCounter () {
counter++;
if (!timeout)
timeout = setTimeout(main, 30*1000);
}
function decreaseCounter() {
counter--;
if (counter === 0)
main();
}
Let's say I have a function:
myFunc = function(number) {
console.log("Booyah! "+number);
}
And I want it to run on a set interval. Sounds like I should use setInterval, huh!
But what if I want to run multiple intervals of the same function, all starting at the exact same time?
setInterval(function(){
myFunc(1);
}, 500);
setInterval(function(){
myFunc(2);
}, 1000);
setInterval(function(){
myFunc(3);
}, 2000);
So that the first runs exactly twice in the time it takes the second to run once, and the same between the second and third.
How do you make sure that they all start at the same time so that they are in sync?
Good question, but in JS you can't. To have multiple functions in the same program execute at the same time you need multi-threading and some deep timing and thread handling skills. JS is single threaded. setInterval doesn't acutally run the function after the delay, rather after the delay it adds the function to the event stack to be run as soon as the processor can get to it. If the proc is busy with another operation, it will take longer than the delay period to actually run. Multiple intervals/timeouts are all adding calls to the same event stack, so they run in turn as the proc is available.
function Timer(funct, delayMs, times)
{
if(times==undefined)
{
times=-1;
}
if(delayMs==undefined)
{
delayMs=10;
}
this.funct=funct;
var times=times;
var timesCount=0;
var ticks = (delayMs/10)|0;
var count=0;
Timer.instances.push(this);
this.tick = function()
{
if(count>=ticks)
{
this.funct();
count=0;
if(times>-1)
{
timesCount++;
if(timesCount>=times)
{
this.stop();
}
}
}
count++;
};
this.stop=function()
{
var index = Timer.instances.indexOf(this);
Timer.instances.splice(index, 1);
};
}
Timer.instances=[];
Timer.ontick=function()
{
for(var i in Timer.instances)
{
Timer.instances[i].tick();
}
};
window.setInterval(Timer.ontick, 10);
And to use it:
function onTick()
{
window.alert('test');
}
function onTick2()
{
window.alert('test2');
}
var timer = new Timer(onTick, 2000,-1);
var timer = new Timer(onTick2, 16000,-1);
For a finite number of ticks, change the last parameter to a positive integer for number. I used -1 to indicate continuous running.
Ignore anyone who tells you that you can't. You can make it do just about any thing you like!
You can make something like this.
arr = Array();
arr[0] = "hi";
arr[1] = "bye";
setTimer0 = setInterval(function(id){
console.log(arr[id])
},1000,(0));
setTimer1 = setInterval(function(id){
console.log(arr[id]);
},500,(1));
Hope it helps!
JavaScript is single threaded. You can use html5 web worker or try using setTimeout recursively. Create multiple functions following this example:
var interval = setTimeout(appendDateToBody, 5000);
function appendDateToBody() {
document.body.appendChild(
document.createTextNode(new Date() + " "));
interval = setTimeout(appendDateToBody, 5000);
}
Read this article:
http://weblogs.asp.net/bleroy/archive/2009/05/14/setinterval-is-moderately-evil.aspx
You can use multiples of ticks inside functions, in the example below you can run one function every 0.1 sec, and another every 1 sec.
Obviously, the timing will go wrong if functions require longer times than the intervals you set. You might need to experiment with the values to make them work or tolerate the incorrect timing.
Set a variable to handle tick multiples
let tickDivider = -1
Increase the value of tick variable inside the faster function
const fastFunc = ()=> {
tickDivider += 1
console.log('fastFunciton')
}
Use a condition to on running the slower function
const slowFunc = ()=> {
if (!(tickDivider % 10)){
console.log('slowFunction')
}
}
Call both functions in a single one. The order is not important unless you set tickDivider to 0 (of any multiple of 10)
const updateAllFuncs = () => {
fastFunc()
slowFunc()
}
Set the interval to the frequency of the faster function
setInterval(updateAllFuncs, 100)
What I'm doing here is adding a speed attribute to the HTML elements. These speeds are passed as a parameter to setCounter(). I did this mainly to make the code easier to test and play with.
The function setCounter() is invoked inside a loop for every HTML element with class counter. This function sets a new setInterval in every execution.
The intervals seem to be working in sync.
const elements = document.querySelectorAll('.counter')
elements.forEach((el, i) => {
let speed = Number(elements[i].getAttribute('speed'))
setCounter(el, speed, 5000)
})
function setCounter(element, speed, elapse){
let count = 0
setInterval(() => {
count = (count >= elapse) ? elapse : count + speed
if(count === elapse) clearInterval()
element.innerHTML = count
}, 1)
}
Same Speeds
<p class="counter" speed='10'></p>
<p class="counter" speed='10'></p>
Different Speeds
<p class="counter" speed='3'></p>
<p class="counter" speed='5'></p>