We Keep Coding

Stopping a key event from firing excessively

I made a simple image gallery with a lightbox-style modal each time the image clicks. (I called it lightbox, but it's not the Lightbox library.) It works and I started getting creative with it, deciding to make the images navigable if I hit the arrow keys while the modal is open.
This almost works. The images usually go back in forth in order. However, sometimes it'll flash to the wrong image before it goes to the right one. I've captured it doing this by using console.log on the index of the array that holds the images. What I see in my console is a bunch of weird numbers between the consecutive numbers. It'll go from the right image, to the right image, but occasionally it'll flicker. It seems to often report those weird numbers, whether it flickers or not. It doesn't always do this, so I'm not entirely sure what the cause is, but I suspect that it's reading "key_up" too many times.
Here's the code:
//Allow for keyboard navigation, only if the lightbox is open.
document.addEventListener("keyup", (event)=> {
if(lightbox) {
if(event.key === "ArrowRight") {
index++;
if(index === images.length) {
index = 0;
}
lb_img.firstElementChild.src = images[index].src;
console.log(index);
}
if(event.key === "ArrowLeft") {
index--;
if(index === -1) {
index = images.length - 1;
}
lb_img.firstElementChild.src = images[index].src;
console.log(index);
}
}
});
If you want the full code, I have it on a gist: https://gist.github.com/jckuhl/f8a56349d29308eb4af207a09787270a
EDIT: gist is updated with the new code.
And here's an example of my console: https://i.imgur.com/uWBMS4J.jpg
Any ideas why it might be doing this?

You are attaching the eventlistener as much times as you have clicked on images, because you attach it inside the eventhandler for the click event. This is causing your trouble.
Make sure you attach it only once, by initializing it outside the for loop and outside the click handler.

SetInterval loop relatively confusing to me

HTML
<div id="backspace" ng-click="deleteString(''); decrementCursor();">
JS
<script>
$scope.deleteString = function() {
if($scope.cursorPosVal > 0){
//$scope.name = $scope.name - letter;
$scope.name = [$scope.name.slice(0, $scope.cursorPosVal - 1) + $scope.name.slice($scope.cursorPosVal)].join('');
console.log($scope.name);
setTimeout(function(){ setCaretPosition("inputBox", $scope.cursorPosVal); }, 30);
} else {
$scope.cursorPosVal = 1;
}
};
</script>
I am designing an on screen touchscreen keyboard. This is my backspace button. I am going to make it so that when you click and hold the backspace button, it starts removing characters automatically. I don't know where to begin with creating a setInterval, and I know a setInterval is exactly what I need to use here.

If I'm not wrong, you want that while you're keeping your button pressed, a function repeats itself.
You're right with setInterval(). However, the way you manage the event is wrong.
Take a look at this fiddle (It's not your code, but a simple example is the best way to understand):
http://jsfiddle.net/daq9atdd/1/
$(function(){
var interval = null;
$('#myButton').mousedown(function(){
interval = setInterval(function(){
console.log('Hello !');
}, 250);
});
$('#myButton').mouseup(function(){
clearInterval(interval);
});
});
I start the interval when the button is pressed, store it, and clear it when the button is released.

You’re so sure about setInterval.
If browser briefly hangs for whatever reason (say some background task), setInterval would go on queueing your backspace calls until it has some CPU time. This means user may see no change and hold backspace longer than needed, and then see a whole bunch of characters suddenly vanish when browser is back to normal.
Thus by setting a timeout after every call you’re making sure user won’t remove more characters than needed. Might be important if the goal is to improve UX.
Example implementation with AngularJS directives and setTimeout
See also:
setTimeout or setInterval?
noKid’s fiddle updated with setTimeout in mind

Can't see problem in JS

I want that when mouse is over an image, an event should be triggered ONCE, and it should be triggered again only after mouse is out of that image and back again, and also at least 2 seconds passed.
If I leave my mouse over the image,it gets called like every milisecond,and by the logic of my function once you hover on the variable 'canhover' becomes 0 until you move mouse out
This code seems to have a bug and I cant see it. I need a new pair of eyes, but the algorithm is kinda logical
Working code :
<script type="text/javascript">
var timeok = 1;
function redotimeok() {
timeok = 1;
}
//
function onmenter()
{
if (timeok == 1)
{
enter();
timeok = 0;
}
}
//
function onmleave()
{
setTimeout(redotimeok, 2000);
leave();
}
//
$('#cashrefresh').hover(onmenter,onmleave);
function enter(){
$("#showname").load('./includes/do_name.inc.php');
$("#cashrefresh").attr("src","images/reficonani.gif");
}
function leave(){
$("#cashrefresh").attr("src","images/reficon.png");
}
</script>

I don't know if this will solve your entire problem (since we don't have a detailed description of what it is), but instead of:
$('#cashrefresh').hover(onmenter(),onmleave());
try:
$('#cashrefresh').hover(onmenter,onmleave);
And the same thing here:
setTimeout(redotimeok, 2000); // just the function name
Also, I don't see where you ever set timeok to zero. Do you mean to set timeok = 0 in onmenter()?

There are two methods in jquery for your problem:
.mouseenter() and .mouseleave()
Check out the demos there.
EDIT:
I thought hover was for mouseover and mouseout, sorry for confusion.
I checked your code again. And it seems that you're changing the image when mouse gets over the image, which forces browser to load the new image and the old image disappears for a very little while till the new one appears and i think this must be triggering both handlers continuosly and you're getting this behaviour.
Try not to change the source of the image, comment out that line and instead console.log("some message") there and see if the message is repeated as much as .load() was fired before.
Hope this helps.

Try changing onmleave function as follows:
function onmleave()
{
setTimeout(redotimeok, 2000);
leave();
}

How can I reveal content and maintain its visibility when mousing to a child element?

I'm asking a question very similar to this one—dare I say identical?
An example is currently in the bottom navigation on this page.
I'm looking to display the name and link of the next and previous page when a user hovers over their respective icons. I'm pretty sure my solution will entail binding or timers, neither of which I'm seeming to understand very well at the moment.
Currently, I have:
$(document).ready(function() {
var dropdown = $('span.hide_me');
var navigator = $('a.paginate_link');
dropdown.hide();
$(navigator).hover(function(){
$(this).siblings(dropdown).fadeIn();
}, function(){
setTimeout(function(){
dropdown.fadeOut();
}, 3000);
});
});
with its respective HTML (some ExpressionEngine code included—apologies):
<p class="older_entry">Older<span class="hide_me">Older entry:
<br />
{title}</span></p>
{/exp:weblog:next_entry}
<p class="blog_home">Blog Main<span class="hide_me">Back to the blog</span></p>
{exp:weblog:prev_entry weblog="blog"}
<p class="newer_entry">Newer<span class="hide_me">Newer entry:
<br />
{title}</span></p>
This is behaving pretty strangely at the moment. Sometimes it waits three seconds, sometimes it waits one second, sometimes it doesn't fade out altogether.
Essentially, I'm looking to fade in 'span.hide_me' on hover of the icons ('a.paginate_link'), and I'd like it to remain visible when users mouse over the span.
Think anyone could help walk me through this process and understand exactly how the timers and clearing of the timers is working?
Thanks so much, Stack Overflow. You guys have been incredible as I walk down this road of learning to make the internet.

If you just want to get it working, you can try to use a tooltip plugin like this one.
If you want to understand how this should be done: first, get rid of the timeout, and make it work without it. The difference (from the user's point of view) is very small, and it simplifies stuff (developing and debugging). After you get it working like you want, put the timeout back in.
Now, the problem is you don't really want to hide the shown element on the navigator mouse-out event. You want to hide it in its own mouse out event. So I think you can just pass the first argument to the navigator hover function, and add another hover to dropdowns, that will have an empty function as a first argument, and the hiding code in its second argument.
EDIT (according to your response to stefpet's answer)
I understand that you DO want the dropdown to disappear if the mouse moves out of the navigator, UNLESS its moved to the dropdown itself. This complicates a little, but here is how it can be done: on both types of items mouse-out event, you set a timer that calls a function that hides the dropdown. lets say the timer is 1 second. on both kind of item mouse-in even, you clear this timer (see the w3school page on timing for syntax, etc). plus, in the navigator's mouse-in you have to show the dropdown.

Another issue with the timer in your code is that it will always execute when mouse-out. Due to the 3 seconds delay you might very well trigger it again when mouse-over but since the timer still exist it will fade out despite you actually have the mouse over the element.
Moving the mouse back and forth quickly will trigger multiple timers.
Try to get it to work without the timer first, then (if really needed) add the additional complexity with the delay (which you must keep track of and remove/reset depending on state).

Here was the final working code, for anyone who comes across this again. Feel free to let me know if I could have improved it in any ways:
$(document).ready(function() {
var dropdown = $('span.hide_me');
var navigator = $('a.paginate_link');
dropdown.hide();
$(navigator).hover(function(){
clearTimeout(emptyTimer);
$(this).siblings(dropdown).fadeIn();
}, function(){
emptyTimer = setTimeout(function(){
dropdown.fadeOut();
}, 500);
});
$(dropdown).hover(function(){
clearTimeout(emptyTimer);
}, function(){
emptyTimer = setTimeout(function(){
dropdown.fadeOut();
}, 500);
});
});

Changing Javascript Focus in onClick event?

Note: A possible solution needs only work in Firefox 3.0, my app doesn't allow access from IE! =)
I have a link that, when clicked, will display a lightbox to the user:
show lightbox
My problem is that when the lightbox is displayed, the focus remains on the link. So if the user presses the up or down keys, they end up scrolling the main document, not the lightbox that is displayed!
I've tried to set the focus to the lightbox element using code like this
function focus_on_lightbox() {
document.getElementById('lightbox_content').focus();
}
This works fine if I type it in the firebug console, but will not work if I include it at the end of the onclick snippet. It appears as though I can't change the focus away from the link from code executed inside the onclick event?
-- Update 1
I've tried something like this before
show lightbox
and I've modified function to add some debugging output, as follows
function focus_on_lightbox() {
console.log('hihi');
console.log(document.activeElement);
document.getElementById('lightbox_content').focus();
console.log(document.activeElement);
}
The output is as follows
hihi
<a onclick="closePopup();lightbox('apartment_detail','11619');focus_on_lightbox();return false;" href="#">
<a onclick="closePopup();lightbox('apartment_detail','11619');focus_on_lightbox();return false;" href="#">
So the focus before I did anything was on the link and after I tried to change the focus it still remained on the link?
Not sure if it matters, but I use ajax to load the lightbox, as follows
new Ajax.Updater(lightbox_content_id, url, {asynchronous:true, evalScripts:true, onLoading:show_lightbox_loading(), onComplete:focus_on_lightbox() });
I tried to set the focus after the ajax complete, but also, no luck.
What am I missing?
I've been trying to make a solution work that was suggested below by trying to set the focus, seeing if I succeeded by checking document.activeElement, if not, wait 100 milliseconds and try again. If I use the following function, it will work
function focus_on_lightbox() {
var seconds_waited = 0
pause(100);
var current_focus = document.activeElement
while (document.getElementById(lightbox_content_id) != current_focus && seconds_waited < 2000)
{
document.getElementById(lightbox_content_id).focus();
console.log(document.activeElement);
pause(100);
current_focus = document.activeElement
seconds_waited += 100;
}
}
However, if I remove the firebug debugging statment console.log, the function stops working!! I have no idea why this would be the case?? Why would outputting a variable to the firebug console affect weather focus is moved to the element or not? Does the console.log statement affect focus? perhaps by bringing the focus to the console debugging window?

I think your problem is calling your focus method after return false. your code should be like that :
<a href="#"
onclick="show_lightbox();focus_on_lightbox();return false;">
show lightbox
</a>

Here is the function that finally worked
function focus_on_lightbox(seconds) {
var seconds_waited
seconds_waited = seconds
document.getElementById(lightbox_content_id).focus();
seconds_waited += 100;
if (document.getElementById(lightbox_content_id) != document.activeElement && seconds_waited < 2000)
setTimeout("focus_on_lightbox(" + seconds_waited + ");", 100);
{
}
}
So why did console.log seem to affect setting the focus? Before I was using this function to pause between attempts of changing the focus.
function pause(milliseconds) {
var dt = new Date();
while ((new Date()) - dt <= milliseconds) { /* Do nothing */ }
}
This causes javascript to constantly be doing something and I think it wasn't giving the document time to render or update or something. The console.log seemed to break this lock and give the page a chance to change its focus.
When I changed approaches to using the timeout to pause between attempts, console.log was no longer needed!
Thanks bmoeskau for pointing me in the right direction.

In my experience, focus issues can sometimes be timing-related (e.g., focus() executes before the element is fully ready to be focused). I'm assuming that the lightbox markup is created dynamically when the show_lightbox function is called? If that's the case you could try adding a slight delay before attempting to focus to see if that's the issue, something like:
setTimeout("focus_on_lightbox();", 10);

Make the element focus itself. On the element's load event, set a timeout of a few ms and then call this.focus();
Else try jQuery.