Is it possible to stop an infinite loop from running at all?
Right now I am doing something like this:
var run = true;
loop ({
if(run) {
whatever
}
}, 30),
Then when I want to stop it I change run to false, and to true when I want to start it again.
But the loop is always running whatever I do. It just not executing the code inside.
Is there a way to stop it completely? and make it start again when I want?
If I am understanding your question correctly, what you need is the break keyword. Here's an example.
SetInterval will give you a loop you can cancel.
setInterval ( "doSomething()", 5000 );
function doSomething ( )
{
// (do something here)
}
Set the interval to a small value and use clearinterval to cancel it
function infiniteLoop() {
run=true;
while(run==true) {
//Do stuff
if(change_happened) {
run=false;
}
}
}
infiniteLoop();
It may not be exactly what you are looking for, but you could try setInterval.
var intervalId = setInterval(myFunc, 0);
function myFun() {
if(condition) {
clearInverval(intervalId);
}
...
}
setInterval will also not block the page. You clear the interval as shown with clearInterval.
Use a while loop
while(run){
//loop guts
}
When run is false the loop exits. Put it in a function and call it when you want to begin the loop again.
The problem is that javascript only has a single thread to run on. This means that while you are infinitely looping nothing else can happen. As a result, it's impossible for your variable to ever change.
One solution to this is to use setTimeout to loop with a very small time passed to it. For example:
function doStuff(){
if(someFlag){
// do something
}
setTimeout(doStuff,1);
}
doStuff();
This will give the possibility for other actions to make use of the thread and potentially change the flag.
Related
I am new to javascript, and I am coding a game.
I would like to break out of the setInterval loop when a condition is met to display a game over screen. My code :
var timer = 0;
var i =0;
fond.onload= function()
{
timer = setInterval(boucle,50);
console.log("break");
}
function boucle()
{
i++;
if(i===4)
{
clearInterval(timer);
}
}
I never reach the break log because just after the clearInterval, the screen is stuck.
Thank you!
I am not sure what fond.onload represents in your code, but if you want the code to run when the page is loaded you should use window.onload or document.onload.
onload is a global event handler bound to all objects that gets executed when that object is loaded. I presume that in your case fond is never loaded as the rest of the code is fine, just never runs. It will run fine if you bind the function to window.onload.
You can read up more on that here
I'm writing a "Game of Life" in javascript. I have all the logic done in a function called doGeneration(). I can repeatedly call this from the console and everything goes as planned, however, if I put it in a while loop the execution blocks the UI and I just see the end result (eventually).
while (existence) {
doGeneration();
}
If I add a setTimeout(), even with a generation limit of say 15, the browser actually crashes (Canary, Chrome).
while (existence) {
setTimeout(function() {
doGeneration();
},100);
}
How can I call doGeneration() once every second or so without blocking the DOM/UI?
You want setInterval
var intervalId = setInterval(function() {
doGeneration();
}, 1000);
// call this to stop it
clearInterval(intervalId);
I would use requestAnimationFrame(doGeneration). The idea of this function is to let the browser decide at what interval the game logic or animation is executed. This comes with potential benefits.
https://hacks.mozilla.org/2011/08/animating-with-javascript-from-setinterval-to-requestanimationframe/
Rather than using setINterval or setTimeout and assume some random time interval will be enough for the UI to update you shoul/could make the doGeneration smart enough to call itself after dom was updated and if the condition of existence is satisfied.
I have a probably really simple question but did not find anything about this or maybe did not find the right words for my problem.
If have a function to be executed on keypress which also changes my variable A - fine, and it works.
But now I want to give an alternative value to my variable A if the keypress event is not happening.
So I'm looking for the correct command for the naive logic of
if ("keypress event happens") {
A = 1
} else {
A = 2
}
Is there any way to do that in js or jquery with simple true/false checks for the key event?
I've been trying and trying and it did not work once.
Usually, the way one solves this problem is with a setTimeout(). You set the timer for N seconds. If the keypress happens, you cancel the timer. If the keypress doesn't happen, the timer will fire giving you your alternate event.
You probably wrap this in some sort of function that you can trigger whenever you want, but you didn't share the overall context so this is just the general idea:
$("#myObj").keypress(function(e) {
if (timer) {
clearTimeout(timer);
}
// process key
});
var timer = setTimeout(function() {
timer = null;
// key didn't happen within the alltoted time so fire the alternate behavior
}, 5000);
what i need is a for or while loop that will re run the code every second
ive tried sleep() but i dont think it is working or i have got it right
Do not try to use a for or while loop for such timed operations. You'll have a hard time with reliable or accurate timing and usually end up railing the CPU, making the computer sluggish.
JavaScript provides the setInterval() function for these kinds of tasks. Also note that Greasemonkey has some caveats about how to use setInterval() and setTimeout().
So the code you want is like:
var timerVar = setInterval (function() {DoMeEverySecond (); }, 1000);
function DoMeEverySecond ()
{
//--- Your code here.
}
//--- When ready to stop the timer, run this code:
clearInterval (timerVar);
timerVar = "";
try
// where yourfunction is a method that contains your loop logic
setTimeout(yourfunction, 1000);
This will invoke the function every 1000 milliseconds without having to embed it into a while or for loop.
put it into your body onload or similar event
i got a problem with setTimeout.. i dont know why this will not work..
$(document).ready(function(){
var counterNum = 0;
function tick()
{
addText(counterNum);
setTimeout('tick()',1000);
counterNum++;
}
function addText(strNum)
{
$("div.counter").empty();
$("div.counter").append(strNum);
}
});
you can check it here for the live preview LINK
and also sir, what is the difference between
setTimeout('tick()',1000);
and
setTimeout(tick(),1000);
?
Try:
$(document).ready(function(){
var counterNum = 0;
function tick()
{
addText(counterNum);
setTimeout(tick,1000);
counterNum++;
}
function addText(strNum)
{
$("div.counter").empty();
$("div.counter").append(strNum+"");
}
tick();
});
The difference between
setTimeout('tick()',1000)
and
setTimeout(tick(), 1000)
is that the second one will not wait 1000ms to execute, but if you changed it to
setTimeout(tick, 1000)
it would be effectively the same. Technically, it would change the scope of where the function was called from.
In the case of passing in a string JavaScript has to evaluate it to run your code. With setTimeOut you should always use a pattern like this:
var self = this;
setTimeout(function(){tick();},1000);
This gives you closure and allows you to get around the fact that using setTimeOut changes what this is to be the global object window (a nastly little surprise for developers the first time they encounter it).
Try that in combination with Fredrik recommendeds and you should be in good shape.