Develop Reference

Javascript, run function for 0.5 seconds then stop (Loop)

I'm running a node server with raspberry pi gpio modules installed. I'm trying to get my ESC to start and run for 0.5 seconds, then I need it to stop for .5 second, then start again in a loop. however if "start" = 0 (Button off) I need the loop to stop completely and set the servo pulse width to 1000 (Motor Stop)
Here is my code, It kinda works. But doesn't stop
var start = new blynk.VirtualPin(4);
start.on('write', function t(start) {
if (start == 1) {
setInterval(function() {
setInterval(function() {
motor.servoWrite(1920);
}, 500);
setInterval(function() {
motor.servoWrite(1000);
}, 1000);
}, 500);
} else {
motor.servoWrite(1000);
}
motor.servoWrite(1000);
});
Could someone show me where I've gone wrong?

Store your interval in a variable
var myInterval = setInterval(function() { [... your code code] },delay);
then to stop it by
clearInterval(myInterval);

var start = new blynk.VirtualPin(4);
motor.servoWrite(1000);
var interval, timeout;
start.on('write', function t(start) {
if (start == 1) {
clearInterval(interval);
clearTimeout(timeout);
interval = setInterval(function() {
motor.servoWrite(1920);
timeout = setTimeout(function() {
motor.servoWrite(1000);
}, 500);
}, 1000);
} else {
clearInterval(interval);
clearTimeout(timeout);
motor.servoWrite(1000);
}
});

I think setInterval might be the wrong thing to use. The setInterval is reoccurring. Where you really just want to run something once, wait, then run something else. Try doing it with setTimeout, it waits for x ms then executes something.
var id = null;
start.on('write', function t(start) {
if(start == 1){
pulse();
}
else {
clearTimeout(id);
motor.servoWrite(1000);
}
});
function pulse() {
servoOn();
id = setTimeout(function(){
servoOff();
id = setTimeout(function(){
pulse();
}, 1000);
}, 500);
}
function servoOn(){
motor.servoWrite(1920);
}
function servoOff(){
motor.servoWrite(1000);
}

clearInterval and set it again after x seconds

I want to do simple interval with with if, It is checking a variable's value and doing a function again().
again function contains clearInterval, i++ and setTimeout to call interval again after x seconds
var speed = 1000;
var wait = 0;
var i = 0;
function init() {
setInterval(function() {
if (i >= 6) i = 0;
if (i == 4) {
wait = 5000;
again(wait);
} else {
document.body.innerHTML = i;
i++;
}
}, speed);
}
function again(time) {
clearInterval(init());
i++;
setTimeout(function() {
setInterval(init(), speed);
}, time);
}
init();
I expect output like this:
1, 2, 3, Waiting x sec's , 5, 1, 2, ...
but code is doing some thing crazy, Its going faster and faster. I don't know why.
Here's a codepen with example (can crash your browser!)
Can you fix it and explain? Thanks

You are not clearing interval but use function inside clearInterval method. Method init which is used has no return statement so clearInterval gets undefined in attribute, so it is not clearing nothing.
Fixed code:
var speed = 1000;
var wait = 0;
var i = 0;
var interval=null;
function init() {
interval = setInterval(function() {
if (i >= 6) i = 0;
if (i == 4) {
wait = 5000;
again(wait);
} else {
document.body.innerHTML = i;
i++;
}
}, speed);
}
function again(time) {
clearInterval(interval);
i++;
setTimeout(function() {
init()
}, time);
}
init();
Function setInterval returns interval id and function clearInterval in attribute should get id of interval which we want to stop, so I created interval variable to save id. I am using this variable in clearInterval.

This is a small example how changing the delay of a setInterval call.
(function iife() {
var timer = null,
counter = 0;
function task() {
counter += 1;
console.log(counter);
// condition: every four reps
if (counter % 4 === 0) {
console.log("changed speed to 4 seconds");
return start(4000);
}
// condition: every seven reps
if (counter % 7 === 0) {
console.log("changed speed to 2 seconds");
return start(2000);
}
}
function start(delay) {
clearInterval(timer);
console.log("runs every " + delay + " miliseconds");
timer = setInterval(task, delay);
}
start(1000);
}());

Changer SetInterval Values After Interval

If I can try to make everyone understand what I am looking for, I am looking for the value of the interval to change to lets say "5000ms" after "1000ms" and then it would go on to the next value such as "2000ms" and repeat all over again! The current code I have is pretty much a stopwatch, It adds the number 1 to a paragraph every 1000ms. Any help is extremely appreciated!
<script>
function myFunction() {
clicks += 1;
}
setInterval(myFunction, 1000);
var clicks = 0;
function myFunction() {
clicks += 1;
document.getElementById("demo").innerHTML = clicks;
// connects to paragraph id
}
</script>
<p id="demo"></p>
<!--connects to getElementById-->

Don't use setInterval - this functions will perform the action in any given interval, which you set once.
Use setTimeout instead. Which performs the action only once after given interval, and then call it again and again with different interval values.

what about this
<script>
var clicks = 0;
myFunction(1000);
function myFunction( currentInterval ) {
clicks ++;
document.getElementById("demo").innerHTML = clicks;
if ( currentInterval == 1000 )
{
currentInterval = 5000;
}
else if ( currentInterval == 5000 )
{
currentInterval = 2000;
}
else
{
currentInterval = 1000;
}
setTimeout( function(){ myFunction( currentInterval ) }, currentInterval );
}
</script>
<p id="demo"></p>

you should try using recursive timeout instead of interval
var timeout = 1000;
var timer;
function startTimer() {
clearTimeout(timer);
timer = setTimeout(function() {
console.log('tick');
startTimer();
}, timeout);
}
startTimer();
// timeout = 2000
// timeout = 500
// clearTimeout(timer); to cancel
<script src="https://getfirebug.com/firebug-lite-debug.js"></script>

This might look a little complicated but you can try something like this:
JSFiddle.
(function() {
var interval = null;
var limit = 5;
function initInterval(callback, index) {
var msToSec = 1000;
if (interval) {
clearInterval();
}
console.log("Delay: ", index)
interval = setInterval(callback, index * msToSec);
}
function clearInterval() {
window.clearInterval(interval);
interval = null;
}
function resetInterval(callback, count) {
clearInterval();
initInterval(callback, count);
}
function main() {
var count = 1;
var notify = function() {
console.log("Hello World: ", count);
var _nextCount = ((count++) % limit) + 1;
if (count < 10) {
resetInterval(notify, _nextCount);
} else {
console.log("Stoping loop...");
clearInterval();
}
}
initInterval(notify, count);
}
main()
})()

clearInterval() not working?

function myFunction(interval) {
var intervalID = window.setInterval(function () {
getdetails();
$('.View').load('alert.php').fadeIn("slow");
}, 3000);
if (interval == 1) {
window.clearInterval(intervalID);
}
}
when I call myFunction with argument 1 then clearInterval() not clear the setInterval().I want setInterval() stop its excution when I call myFunction with argument 1.

The problem is that you are creating a new timer everytime you call the function. Modify it like:
var intervalID = 0;
function myFunction(interval){
if(interval == 1) {
if(intervalID != 0) {
window.clearInterval(intervalID);
intervalID = 0;
}
}
else if(intervalID == 0) { // create only if not existing
intervalID = window.setInterval(function () {
...
});
}
}
Now, the firts time you call it, it will create the timer. Afterwards when you call it with 1 as the argument, it will clear the timer.

jQuery reset setInterval timer

My Jquery:
function myTimer() {
var sec = 15
var timer = setInterval(function() {
$('#timer').text(sec--);
if (sec == -1) {
clearInterval(timer);
alert('done');
}
} , 1000);
}
$("#knap").click(function() {
myTimer();
});
$("#reset").click(function() {
// set timer to 15 sec again..
});
I want the timer to be reset when clicked on #reset.

You need to leave your "timer" variable in a scope that is available the next time you call the myTimer function so you can clear the existing interval and reset it with a new interval. Try:
var timer;
functionn myTimer() {
var sec = 15
clearInterval(timer);
timer = setInterval(function() {
$('#timer').text(sec--);
if (sec == -1) {
clearInterval(timer);
alert('done');
}
} , 1000);
}
$("#knap").click(function() {
myTimer();
});
$("#reset").click(function() {
myTimer();
});

or you could do something along these lines:
var myTimer = function(){
var that = this,
time = 15,
timer;
that.set = function() {
console.log('setting up timer');
timer = setInterval(function(){
console.log('running time: ' + time);
},1000);
}
that.reset = function(){
console.log('clearing timer');
clearInterval(timer);
}
return that;
}();
and run when you need to:
myTimer.set();
myTimer.reset();

Clear the timer every time it's initalized, that way all you have to do is call the function again to reset the timer :
var timer;
function myTimer(sec) {
if (timer) clearInterval(timer);
timer = setInterval(function() {
$('#timer').text(sec--);
if (sec == -1) {
clearInterval(timer);
alert('done');
}
}, 1000);
}
$("#knap, #reset").click(function() {
myTimer(15);
});
FIDDLE

You could re-write your myTimer() function like so:
function myTimer() {
var sec, timer = null;
myTimer = function() {
sec = 15;
clearInterval( timer );
timer = setInterval(function() {
$('#timer').text(sec--);
if (sec == -1) {
clearInterval(timer);
alert('done');
}
} , 1000);
};
myTimer();
}
Now, whenever you call myTimer(), the setInterval gets reset.

Here's an approach that is more in tune with the way JS was designed (as a functional language for those who still don't know). Rather than relying on a global variable, use a closure:
$("#knap").click(function start()//named callback to bind && unbind:
{
$(this).unbind('click');//no need to start when started
$("#reset").unbind('click').click((function(timer)
{//timer is in scope thanks to closure
return function()
{//resets timer
clearInterval(timer);
timer = null;
$('#knap').click(start);//bind the start again
//alternatively, you could change the start button to a reset button on click and vice versa
}
})(setInterval((function(sec)
{
return function()
{
$('#timer').text(sec--);
if (sec === -1)
{
$('#reset').click();//stops interval
$('#reset').unbind('click');//no more need for the event
alert('done');
}//here's the interval counter: 15, passed as argument to closure
})(15),1000)));//set interval returns timer id, passed as argument to closure
});
Now I will admit this is rather messy (and untested) but this way there reset event is only available when it's necessary, and you're not using any globals. But crucially, this is where JS's power lies: functions as 1st class objects, passing them as arguments and return values... just go function-crazy :)
I've set up a working Fiddle, too

You could also use a jQuery timer plugin, then you don't need to pass around the Variable.
Plugin: http://archive.plugins.jquery.com/project/timers
Example for the plugin: http://blog.agrafix.net/2011/10/javascript-timers-mit-jquery/