My draw() function stops executing after calling this.circle(). If I call the draw() method directly, it works perfectly. However, if I use setInterval(this.draw, 1000), it seems to return right when calling this.circle(). circle() is never executed either. Am I misusing setInterval?
function Ball() {
this.start = function() {
return setInterval(this.draw, 1000);
}
this.circle = function() {
console.log('1');
}
this.draw = function() {
console.log('2');
this.circle();
console.log('3');
}
this.circle() is never executed, and console.long('3') (or anything after it) is never reached.
The result is console.long('2') being repeatedly printed every 1 second
When you use setInterval, this will refer to window. window doesn't have a function called draw, so it will throw an error and stop execution. To fix it, you need to bind the value of this.
return setInterval(this.draw.bind(this), 1000);
“this” is no longer what you think it is, and you have lost context to it, it no longer represents Ball like you’d like it to. You can bind your draw function like “this.draw.bind(this)” or you can capture “this” using a line like “const _this = this;” and then only reference “_this” in your functions to make sure you are always accessing the correct one.
Some reading on the closures
https://javascript.info/closure
As stated by #iagowp this will refer to the window when your method is called by setInterval. Instead, you can fix this by using an ES6 arrow function to call this.draw(). This way your this is referring to the Ball object rather than the function which called this.draw().
See working example below:
function Ball() {
this.start = function() {
return setInterval(_ => this.draw(), 1000);
}
this.circle = function() {
console.log('1');
}
this.draw = function() {
console.log('2');
this.circle();
console.log('3');
}
}
let b = new Ball();
b.start();
Related
I recently started learning javascript to help maintain some stuff and ran into this issue today:
this.moveChar = function(){
// body here
setTimeout(moveChar,1000);
}
this.initialise= function(){
this.moveChar();
}
When initialise is called, I expected moveChar to be called, then repeated call itself once every 1000ms
However, what actually happens is moveChar gets called once then that's it. Based on other stackoverflow posts I read, I suspected it might be something to do with the function being expressed rather than declared. I have tried to use
this.moveChar = function recMove(){
// body here
setTimeout(recMove,1000);
}
without luck either.
Any suggestions on how I can fix this?
EDIT: Main thing I need to do is have the moveChar function called once every second. If there is a better approach than setTimeout recursion, I'm open to it
this.moveChar is not the same as moveChar, unless this is the global scope object like window.
this.moveChar is a property on an object, while moveChar would reference any variable in a visible scope chain.
You can change it to a couple of things in order to keep scope of whatever object is being used:
Using an arrow function
this.moveChar = function(){
// body here
setTimeout(()=>this.moveChar(),1000);
}
Using .bind()
this.moveChar = function(){
// body here
setTimeout(this.moveChar.bind(this),1000);
}
You might want to consider using setInterval() which is the more appropriate API for this task.
What setInterval() does is - it will repeatedly call the given function upon a certain interval is reached.
See:
https://developer.mozilla.org/en-US/docs/Web/API/WindowTimers/setInterval
Quote:
Repeatedly calls a function or executes a code snippet, with a fixed
time delay between each call. Returns an intervalID.
Example:
Assuming moveChar() contains your operation logic. Then to repeat it you'll do this 1 line.
let moveChar = function(){
// Do stuff
console.log("Hi thanks for calling me!");
}
setInterval(moveChar, 1000);
Are you using this in side body here?
If so, you should bind correct context while call.
this.moveChar = function(){
// body here
setTimeout(this.moveChar.bind(this), 1000);
}
Or use anonymous function:
this.moveChar = function(){
// body here
var that = this;
setTimeout(function(){
that.moveChar();
}, 1000);
}
Or arrow function:
this.moveChar = function(){
// body here
setTimeout(() => this.moveChar(), 1000);
}
Same notes apply to setInterval variant:
this.initialise= function(){
setInterval(this.moveChar.bind(this), 1000);
// var that = this;
// setInterval(function(){that.moveChar();}, 1000);
// setInterval(() => this.moveChar(), 1000);
}
this.moveChar = function(){
// body here
alert('called moveChar');
}
this.initialise= function(){
setInterval(function(){moveChar();},1000);
}
this.initialise();//call here
It might be a beginner question but I'm facing with the next situation:
$(function f() {
function test2() {
//.....
}
function GetData() {
//.....
}
function update() {
test2();
GetData();
//...
}//end update
update();
});//end f()
function stop() {
clearInterval(multipleCalls);
}
function start() {
multipleCalls=null; //this is a global variable
setTimeout(update, 1000);
}
The stop function stops a graphic when a button is pressed and everything works fine. The start function should restart a graphic when a button is pressed. My guess is that the update function is not well invoked in start function. How could I do so everything to work fine?
You have currently commented out the } that closes the update function, so the line that says end f doesn't in fact end f(). In its present state, your code would not execute. (I note that someone else edited your code after which this remark is no longer valid; I don't know if the edit is closer to your actual code, or if it did in fact obscure a real error)
You're referring to both multiplecalls and multipleCalls. Note that javascript is case sensitive.
You're clearing multipleCalls but never setting it to anything but null. Did you intend to write multipleCalls = setTimeout(update, 1000) ?
start, being placed outside of f, won't have access to update. Either define update and the functions it is dependent upon outside of f(), or make it globally accessible, i.e.
window.update = function() { ... }
Which you'd then be able to access as setTimeout(window.update, 1000);
You have a scoping issue. The update is only known within the f.
You are trying to call it from outside f in start. The only way to achieve this is to either expose function update to the same scope as where start is, or bring start to the same scope as update.
The first option is easiest (and ugliest):
function update() {
//...
}
// assign it to the global scope (window is the global scope for browsers)
window.update = update;
Now update is available from `starts.
The more appropriate approach would be to define your handlers (which call start and stop within the scope of f, for example
$(function f() {
//.. everything there now
$('.start').on('click', function(e) {
setTimeout(update, 1000);
});
});
Working example
$(function f() {
var timer; // no need to be 'global'
function update() {
$('.result').text(new Date() + ' GetData();');
}
$('.start').on('click', function() {
// always clear a timer before setting it
clearTimeout(timer);
// and always set a timer variable, so it can be cancelled
timer = setTimeout(update, 1000);
});
$('.stop').on('click', function() {
// cancel the timer
clearTimeout(timer);
});
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button class=start>start</button>
<button class=stop>stop</button>
<div class=result>..</div>
You could try this:
window.update = function update() {...}
and then:
setTimeout(window.update, 1000);
I'm trying to figure out how I can reset a timer created inside of an immediately invoking function from within the setTimeout closure. Here is my function:
var triggerHeightRecalc = function() {
setTimeout(function() {
if(imagesLoaded()) {
adjustHeight();
} else {
triggerHeightRecalc();
}
}, 100);
}();
In the event that imagesLoaded() returns false, I receive the following error from attempting to call triggerHeightRecalc():
Uncaught TypeError: undefined is not a function
So I'm not sure if the issue is the function is not in the scope, or maybe it just cannot call itself? I've tried passing triggerHeightRecalc as a parameter in the setTimeout closure, but that doesn't seem to work either.
I've also tried this after reading this SO question:
var triggerHeightRecalc = function() {
var that = this;
var callback = function() {
if(imagesLoaded()) {
adjustHeight();
} else {
that.triggerHeightRecalc();
}
};
timeDelay = window.setTimeout(callback, 100);
}();
What am I doing wrong here, or is there a better way? Is this something that should be a setInterval() instead and I clear the interval when images are loaded?
Side Note: I'm calculating the height of a div inside a jQuery plugin, but I need to wait until the images are loaded in order to get the correct height (not sure if that is relevant).
Since you are invoking the function right from the declaration triggerHeightRecalc is getting set to the return of that function call, which is undefined since you in fact do not return anything.
You can do two things
1. Declare then invoke
var triggerHeightRecalc = function() {
setTimeout(function() {
if(imagesLoaded()) {
adjustHeight();
} else {
triggerHeightRecalc();
}
}, 100);
};
triggerHeightRecalc();
2. Wrap the declaration in () and invoke
var triggerHeightRecalc;
(triggerHeightRecalc = function() {
setTimeout(function() {
if(imagesLoaded()) {
adjustHeight();
} else {
triggerHeightRecalc();
}
}, 100);
})();
The second one will create a global variable unless you do the var triggerHeightRecalc; before hand.
Already answered, but I'll put this in.
First of all, if you just want to wait until all images have loaded you can use:
https://github.com/desandro/imagesloaded and then run the above code.
If that's not what you want, and you you just want a function that your setTimeout can run, then you can remove the () at the end of the function.
Here is what's happening in your current code
Your function is missing the opening bracket or similar character !+( (function.
Also your IIFE has no return keyword, and will return undefined to triggerHeightCalc.
If you do want an IIFE then you can either have a private version that is only callable within itself.
(function myModule(){
myModule(); //calls itself
})();
Or a public version that can be called both inside and outside.
var myModule = (function(){
return function myMod(){
myMod();
}
})();
myModule();
Patrick Evans has the right reasons, but there is a neater way to solve it :)
(function triggerHeightRecalc() {
setTimeout(function() {
if(imagesLoaded()) {
adjustHeight();
} else {
triggerHeightRecalc();
}
}, 100);
})();
Here you are give an internal name to the (still) anonymous function. The name is only visible from within the function itself, its not visible in the global scope. Its called a Named function expression.
I have the following code:
function fn($){
return function(){
innerFn = function(){
setTimeout(show, 1000);
};
show = function(){
$.alert("TEST");
}
}
}
But, after one second, when the function show is run, it says $ is undefined. How do I resolve this issue?
how to pass arguments to a function in setTimeout
setTimeout has a built in mechanism for adding params
var timeoutID = window.setTimeout(func, delay, [param1, param2, ...]);
use it.
If you're going to use this - you should be careful. but that's another question.
There are a number of things at play here. The most important being that your setTimeout never gets called, since innerFn never gets called. This should do the trick.
function fn($){
return function(){
setTimeout(function(){
$.alert("TEST");
}, 1000);
}
}
fn(window)(); //triggers your alert after 1000ms
Your code makes no any sense, because nothing is called:
function fn($){
return function(){
innerFn = function(){
setTimeout(show, 1000);
};
show = function(){
$.alert("TEST");
}
}
}
Let's say I'm calling fn passing window, then a function is returned, that I can executed. But because this function is containing only function declaration - you also forget var so you pollute the global scope, that is bad - nothing is happen.
You'll need at least one function call inside, like:
function fn($){
return function(){
var innerFn = function(){
setTimeout(show, 1000);
};
var show = function(){
$.alert("TEST");
}
innerFn();
}
}
fn(window)();
And that will works. However, it's definitely redundant. You can just have:
function fn($){
return function(){
function show(){
$.alert("TEST");
}
setTimeout(show, 1000);
}
}
To obtain the same result. However, if you're goal is just bound an argument to setTimeout, you can use bind. You could use the 3rd parameter of setTimeout as the documentation says, but it seems not supported in IE for legacy reason.
So, an example with bind will looks like:
function show() {
this.alert('test');
}
setTimeout(show.bind(window), 1000);
Notice also that window is the global object by default, so usually you do not have to do that, just alert is enough. However, I suppose this is not your actual code, but just a mere test, as the alert's string says.
If you prefer having window as first parameter instead, and you're not interested in the context object this, you can do something like:
function show($) {
$.alert('test');
}
setTimeout(show.bind(null, window), 1000);
I'm writing a JavaSCript class that has a method that recursively calls itself.
Scheduler.prototype.updateTimer = function () {
document.write( this._currentTime );
this._currentTime -= 1000;
// recursively calls itself
this._updateUITimerHandler = window.setTimeout( arguments.callee , 1000 );
}
Property description:
_currentTime: the currentTime of the timer in miliseconds.
_updateUITimerHandler: stores the reference so can be used later with clearTimeout().
my problem is where I'm using recursion with setTimeout(). I know setTimeout() will accept some string to execute, or a reference to a function. since this function is method of an object, I don't know how to call it from outside. so I used the second format of setTimeout() and passed in a reference to the method itself. but it does not work.
Try this:-
Scheduler.prototype.startTimer = function() {
var self = this;
function updateTimer() {
this._currentTime -= 1000;
self.hTimer = window.setTimeout(updateTimer, 1000)
self.tick()
}
this.hTimer = window.setTimeout(updateTimer, 1000)
}
Scheduler.prototype.stopTimer = function() {
if (this.hTimer != null) window.clearTimeout(this.hTimer)
this.hTimer = null;
}
Scheduler.prototype.tick = function() {
//Do stuff on timer update
}
Well the first thing to say is that if you're calling setTimeout but not changing the interval, you should be using setInterval.
edit (update from comment): you can keep a reference from the closure if used as a class and setInterval/clearInterval don't require re-referencing.
edit2: it's been pointed out that you wrote callee which will work quite correctly and 100% unambiguously.
Out of completeness, this works:
function f()
{
alert('foo');
window.setTimeout(arguments.callee,5000);
}
f();
so I tried out document.write instead of alert and that is what appears to be the problem. doc.write is fraught with problems like this because of opening and closing the DOM for writing, so perhaps what you needed is to change the innerHTML of your target rather than doc.write
You could hold a pointer towards it...
/* ... */
var func = arguments.callee;
this._updateUITimerHandler = window.setTimeout(function() { func(); }, 1000);
/* ... */