Alternative action if event does not occur javascript/jquery - javascript

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);

Related

How to kill a Javascript function if it is called again?

I have a search box on my web page that has check boxes in order for the user to filter their results. Only one check box can be checked at once.
When a check box is clicked my code runs off and applies the filter to the list and returns the correct results.
The problem I have is that when a check box is clicked multiple times in quick succession, it queues the requests and pulls them back one by one. This can take a while if a check box is checked and then un-checked multiple times.
Is there any way in Javascript to inform the function that it has been called again and it should stop everything other than this last request?
You want to wrap your onclick callback in a debouncing function like
http://underscorejs.org/#debounce
Say you have this
function search() {
// ...
}
$jquery(".myFilterCheckboxes").click(search);
You should be able to just change the above to:
// Only allow one click event / search every 500ms:
$jquery(".myFilterCheckboxes").click(_.debounce(search, 500));
There are tons of debouncing functions out there, and writing your own isn't a big deal really if you can't or don't want to include underscore.js.
My first thought was towards debouncing because you mentioned multiple clicks creating multiple events in a short period. Debouncing is used really often for things like type-ahead search or autocomplete to provide a little space between key presses for thinking time.
As others have mentioned it may make more sense to simply disable the checkboxes / click event while your search is running. In that case, try something like this:
function disableClick(elem) {
elem.unbind("click");
elem.attr("disabled", true);
}
function enableClick(elem, onclick) {
// Enable click events again
elem.live("click", search);
// Enable the checkboxes
elem.removeAttr("disabled");
}
function search() {
var boxes = $jquery(".myFilterCheckboxes");
disableClick(boxes);
$.get(...).always(function() {
enableClick(boxes, search);
});
}
$jquery(".myFilterCheckboxes").live("click", search);
Why disable the click event, add the disabled attribute to the checkboxes instead of just a global lock variable? Well, global locks can be somewhat error prone, but more than that, we already have a global object that matters in the DOM. If we just modify the DOM state we get the right behavior and signal to our users that they should chill out on the checkboxes until the search completes.
That said, it probably makes sense with any kind of locking / unbinding scenario to indicate to the user with a loading spinner or something that you're doing work.
You can use a lock pattern:
http://jsfiddle.net/RU6gL/
HTML
<input type="checkbox" onclick="fire()" >CB1
<br />
<input type="checkbox" onclick="fire()" >CB2
JS
function_lock = false
fire = function() {
// First, check the lock isn't already reserved. If it is, leave immediately.
if (function_lock) return;
// We got past the lock check, so immediately lock the function to
// stop others entering
function_lock = true;
console.log("This message will appear once, until the lock is released")
// Do your work. I use a simple Timeout. It could be an Ajax call.
window.setTimeout(function() {
// When the work finishes (eg Ajax onSuccess), release the lock.
function_lock = false;
}, 2000);
}
In this example, the function will only run once, no matter how many times the checkboxes are clicked, until the lock is released after 2 seconds by the timeout.
This pattern is quite nice, because it gives you control opver when you release the lock, rather than relying on a timed interval like 'debounce'. For example, it will work with Ajax. If your checkbox is triggering an Ajax call to do the filtering, you can:
On first click, set the lock
Call the Ajax endpoint. Subsequent clicks won't call the Ajax endpoint.
In the Ajax success function, reset the lock.
The checkboxes can now be clicked again.
HTML
<input type="checkbox" onclick="doAjax()" >CB2
JS
ajax_lock = false
doAjax: function() {
// Check the lock.
if (ajax_lock) return;
// Acquire the lock.
ajax_lock = true;
// Do the work.
$.get("url to ajax endpoint", function() {
// This is the success function: release the lock
ajax_lock = false;
});
}
The issue here is that the checkbox is repeatedly clicked on. You should instead disable your checkbox(which would also disable the click event on the element) when you are processing and then re-enable your checkbox when you're done processing.
The debouncing is a great idea, but you don't always know how long it will take for your processing function to finish.
Here's a simple example using jquery promise to re-enable the checkbox after some processing
http://jsfiddle.net/94coc8sd/
with the following code:
function processStuff() {
var dfd = $.Deferred();
// do some processing, when finished,
// resolve the deferred object
window.setTimeout(function(){
dfd.resolve();
}, 2000);
return dfd.promise();
}
function startProcessing() {
$('#processingCheckbox').attr('disabled', 'disabled');
var promise = processStuff();
promise.done(enableCheckbox);
}
function enableCheckbox() {
$('#processingCheckbox').removeAttr('disabled');
}
$('#processingCheckbox').on('click', startProcessing);

An efficient way to cancel a mouseover event... read on to see why

I'm in the process of authoring a completely client side web language reference site. A problem that I encountered today; I have a side panel that is a unordered list of terms and they have onmouseover event listeners. I decided it would be a good idea to add a delay prior to execution and cancel the event at run-time if the mouse was no longer over that element. This is what I've come up with but I feel there must be a better way.
var currentXCoordinate=0
var currentYCoordinate=0
var elementFromCurrentMousePosition=0
function trackCurrentMousePosition(event) {
if (document.elementFromPoint(event.clientX, event.clientY).nodeName=="SPAN") {
elementFromCurrentMousePosition=document.elementFromPoint(event.clientX, event.clientY).parentNode
}
else {
elementFromCurrentMousePosition=document.elementFromPoint(event.clientX, event.clientY)
}
return (currentXCoordinate=event.clientX, currentYCoordinate=event.clientY, elementFromCurrentMousePosition)
}
function initPreview(event, obj) {
arg1=event
arg2=obj
setTimeout("setPreviewDataFields(arg1, arg2)", 100)
}
function setPreviewDataFields(event, obj) {
if ('bubbles' in event) {
event.stopPropagation()
}
else {
event.cancelBubble=true
}
if (elementFromCurrentMousePosition!=obj) {
return 0;
}
The code goes on to do all the wonderful stuff I want it to do if execution wasn't cancelled by the previous if statement. The problem is this method is seeming to be really processor intensive.
To sum it up: on page load all my event listeners are registered, cursor position is being tracked by a onmousemove event. Applicable list items have a onmouseover event that calls the initPreview function which just waits a given period of time before calling the actual setPreviewDataFields function. If at run-time the cursor is no longer over the list element the function stops by return 0.
Sadly that's the best I could come up with. If anyone can offer up a better solution I would be very grateful.
Why not just use mouseout to tell when the mouse leaves an element? Running all of that code every time the mouse moves isn't ideal.
Also, you really shouldn't pass a string to setTimeout like that. Instead, pass a function. As a bonus, you can get rid of those evil global variables arg1 and arg2. With those being globals, I think you will run into issues if init gets called again before the timeout expires.

Javascript timeout when no actions from user for specified time

I want to call a js function when there is no activity from user on the web page for specified amount of time. If there is activity from user then reset timeout. I tried to search but couldn't find anything in particular. I am familiar with setTimeout() and clearTimeout() and how they work. What I am looking for is where/how to monitor for user activity. Is there any event in which I can set and clear timer?
Thank you.
Edit #1:
This webpage has one input text box & one button. It's kind of regular chat page. When I say no user activity, I mean that the user has not typed anything in text box or has not pressed any button for specified amount of time. And one more thing that it is targeted for touch based smartphone devices.
Edit #2:
Thank you everyone for suggestions. I've implemented solution based on more than one answers provided. So I will give upvote to all answers that I've found helpful instead of accepting one as answer.
// Using jQuery (but could use pure JS with cross-browser event handlers):
var idleSeconds = 30;
$(function(){
var idleTimer;
function resetTimer(){
clearTimeout(idleTimer);
idleTimer = setTimeout(whenUserIdle,idleSeconds*1000);
}
$(document.body).bind('mousemove keydown click',resetTimer); //space separated events list that we want to monitor
resetTimer(); // Start the timer when the page loads
});
function whenUserIdle(){
//...
}
Edit: Not using jQuery for whatever reason? Here's some (untested) code that should be cross-browser clean (to a point; doesn't work on IE5 Mac, for example ;):
attachEvent(window,'load',function(){
var idleSeconds = 30;
var idleTimer;
function resetTimer(){
clearTimeout(idleTimer);
idleTimer = setTimeout(whenUserIdle,idleSeconds*1000);
}
attachEvent(document.body,'mousemove',resetTimer);
attachEvent(document.body,'keydown',resetTimer);
attachEvent(document.body,'click',resetTimer);
resetTimer(); // Start the timer when the page loads
});
function whenUserIdle(){
//...
}
function attachEvent(obj,evt,fnc,useCapture){
if (obj.addEventListener){
obj.addEventListener(evt,fnc,!!useCapture);
return true;
} else if (obj.attachEvent){
return obj.attachEvent("on"+evt,fnc);
}
}
This calls for a debouncer:
function debounce(callback, timeout, _this) {
var timer;
return function(e) {
var _that = this;
if (timer)
clearTimeout(timer);
timer = setTimeout(function() {
callback.call(_this || _that, e);
}, timeout);
}
}
Used like this:
// we'll attach the function created by "debounce" to each of the target
// user input events; this function only fires once 2 seconds have passed
// with no additional input; it can be attached to any number of desired
// events
var userAction = debounce(function(e) {
console.log("silence");
}, 2000);
document.addEventListener("mousemove", userAction, false);
document.addEventListener("click", userAction, false);
document.addEventListener("scroll", userAction, false);
The first user action (mousemove, click, or scroll) kicks off a function (attached to a timer) that resets each time another user action occurs. The primary callback does not fire until the specified amount of time has passed with no actions.
Note that no global flags or timeout variables are needed. The global scope receives only your debounced callback. Beware of solutions that require maintenance of global state; they're going to be difficult to reason about in the context of a larger application.
Note also that this solution is entirely general. Beware of solutions that apply only to your extremely narrow use case.
Most JavaScript events bubble, so you could do something like the following:
Come up with a list of all the events you'd consider to be "activity from the user" (e.g., click, mousemove, keydown, etc.)
Attach one function as an event listener for all of those events to document (or maybe document.body for some of them; I can't remember if that's an issue or not).
When the listener is triggered, have it reset the timer with clearTimeout/setTimeout
So you'd end up with something like this:
var events = ['click', 'mousemove', 'keydown'],
i = events.length,
timer,
delay = 10000,
logout = function () {
// do whatever it is you want to do
// after a period of inactivity
},
reset = function () {
clearTimeout(timer);
timer = setTimeout(logout, 10000);
};
while (i) {
i -= 1;
document.addEventListener(events[i], reset, false);
}
reset();
Note that there are some issues you'd have to work out with the above code:
It's not cross-browser compatible. It only uses addEventListener, so it won't work in IE6-8
It pollutes the global namespace. It creates a lot of excess variables that might conflict with other scripts.
It's more to give you an idea of what you could do.
And now there are four other answers, but I've already typed it all up, so there :P
You want to monitor events like mousemove, keypress, keydown, and/or click at the document level.
Edit: This being a smartphone app changes what events you want to listen for. Given your textbox and button requirements, I'd listen to oninput and then add the resetTimeout() call to the click handler for your button.
var inactivityTimeout = 0;
function resetTimeout() {
clearTimeout(inactivityTimeout);
inactivityTimeout = setTimeout(inactive, 300000);
}
function inactive() {
...
}
document.getElementById("chatInput").oninput = resetTimeout;
Something like this:
function onInactive(ms, cb){
var wait = setTimeout(cb, ms);
// Bind all events you consider as activity
// Note that binding this way overrides any previous events bound the same wa
// So if you already have events bound to document, use AddEventListener and AttachEvent instead
document.onmousemove = document.mousedown = document.mouseup = document.onkeydown = document.onkeyup = document.focus = function(){
clearTimeout(wait);
wait = setTimeout(cb, ms);
};
}
IE: http://jsfiddle.net/acNfy/
Activity in the bottom right frame will delay the callback.
I'm using a nifty little 'delay' method for this that I found in this thread
var delay = (function(){
var timer = 0;
return function(callback, ms){
clearTimeout (timer);
timer = setTimeout(callback, ms);
};
})();
use like
delay(function(){ doSomethingWhenNoInputFor400ms(); },400);
Also, take a look at jQuery idleTimer plugin from Paul Irish (jquery.idle-timer.js). It was based on Nicholas C. Zakas' Detecting if the user is idle with JavaScript and YUI 3 article (idle-timer.js).
It looks at similar events to the other answers, plus a few more.
events = 'mousemove keydown DOMMouseScroll mousewheel mousedown touchstart touchmove';
// activity is one of these events

Auto submit form after x mili seconds of inactive keyboard

In my form I have a set of input boxes where a user can input a value.
On change of one of these boxes, the form automatically gets submitted.
The problem now is however that a user stays in the last field, takes the mouse and presses the OK button (of another form) without leaving the textbox first. The change event doesn't get triggered and the old, incorrect values get passed to the next page.
I want to trigger the onchange event after a few miliseconds of inactive keyboard. Just like most autocomplete plugins do.
I think I could implement a timer that starts timing the moment you enter an input field and gets resetted everytime a keystroke is handled and then when it reaches zero the onchange event gets triggered.
I'm not up for re-inventing the wheel and was wondering if such a function is available somewhere.
Suggestions?
I had a similar problem and created a jQuery plugin currently in use in an internal application. It should trigger the change event after the user is done typing.
If you are not using jQuery, the code is still adaptable to anything else.
jQuery.fn.handleKeyboardChange = function(nDelay)
{
// Utility function to test if a keyboard event should be ignored
function shouldIgnore(event)
{
var mapIgnoredKeys = {
9:true, // Tab
16:true, 17:true, 18:true, // Shift, Alt, Ctrl
37:true, 38:true, 39:true, 40:true, // Arrows
91:true, 92:true, 93:true // Windows keys
};
return mapIgnoredKeys[event.which];
}
// Utility function to fire OUR change event if the value was actually changed
function fireChange($element)
{
if( $element.val() != jQuery.data($element[0], "valueLast") )
{
jQuery.data($element[0], "valueLast", $element.val())
$element.trigger("change");
}
}
// The currently running timeout,
// will be accessed with closures
var timeout = 0;
// Utility function to cancel a previously set timeout
function clearPreviousTimeout()
{
if( timeout )
{
clearTimeout(timeout);
}
}
return this
.keydown(function(event)
{
if( shouldIgnore(event) ) return;
// User pressed a key, stop the timeout for now
clearPreviousTimeout();
return null;
})
.keyup(function(event)
{
if( shouldIgnore(event) ) return;
// Start a timeout to fire our event after some time of inactivity
// Eventually cancel a previously running timeout
clearPreviousTimeout();
var $self = $(this);
timeout = setTimeout(function(){ fireChange($self) }, nDelay);
})
.change(function()
{
// Fire a change
// Use our function instead of just firing the event
// Because we want to check if value really changed since
// our previous event.
// This is for when the browser fires the change event
// though we already fired the event because of the timeout
fireChange($(this));
})
;
}
Usage:
$("#my_input").handleKeyboardChange(300).change(function()
{
// value has changed!
});
Does it not work to do an onBlur, so both when the user moves to the next field or clicks something else, the value is saved?
I don't know that such a solution would be considered "re-inventing" anything. As you said, it sounds to be nothing more than a simple setTimeout once the page loads. After about 3,000 milliseconds, it runs form.submit().
I would probably restart the count-down with each keystroke too, to give the user enough time to make their entry.

capture multiple "onkeydown" and wait until "onkeyup" to execute

In my web app, I use the onkeydown event to capture key strokes.
For example, I capture the 'j' key to animate a scroll down the page (and do some other stuff meanwhile).
My problem is the user might keep the 'j' key down to scroll further down the page (this is equivalent to fast multiple key strokes).
In my app, this result in a series of animations that doesn't look that good.
How can I know when the key has been released, and know the amount of key stokes I should have captured? This way I could run one long animation instead of multiple short ones.
Building on #JMD:
var animate = false;
function startanimation()
{
animate = true;
runanimation();
}
function stopanimation()
{
animate = false;
}
function runanimation()
{
if ( animation_over )
{
if ( !animate )
{
return;
}
return startanimation();
}
// animation code
var timeout = 25;
setTimeout(function(){runanimation();},timeout);
}
document.onkeydown = startanimation;
document.onkeyup = stopanimation;
You'll need to add some checks for starting/ending animations, however.
Edit: added a return to the JS; would've recursed endlessly.
Rather than trying to stack up the animations, you could start an animation on keyDown, and if at the end of the animation you haven't yet received keyUp then start another animation. As soon as you reach the end of an animation and you do have keyUp then you're done.
setTimeout returns a timer ID. So what I would do is after you receive a keyDown event, I would start a timer with a very short wait period, like so:
var globalTimerId = -1;
var keyDownCount = 0;
function handleKeyDown(e) {
if (globalTimerId != -1) {
clearTimeout(globalTimerId);
keyDownCount++;
}
/* 500 means 1/2 a second, adjust for your needs */
globalTimerId = setTimeout(handleKeyDownAfterWait, 500);
keyDownCount = 1;
}
function handleKeyDownAfterWait() {
globalTimerId = -1;
/* keyDownCount will have the number of times handleKeyDown was called */
}
So the idea is that each time a keyDown event is received, the timer is cleared (assuming it hasn't elapsed yet) and restarted. If the timer expires, the user has let go of the key and you can handle that in handleKeyDownAfterWait.
There may be other more elegant solutions with jQuery or another JS library however. This is just something quick and dirty (and possibly buggy ;))
you can try using my repsonsiveness plugin see:
http://notetodogself.blogspot.com/2008/12/jquery-responsiveness-plugin-for-fast.html
see the demo here:
http://doesthatevencompile.com/current-projects/jquery.responsiveness/
the one where you type stuff fast. you can adapt that to your needs. like so:
the animation event will be bound with the plugin, and execute when the user stops doing something fast. you can count how many times he does the fast thing by normal binding of the event.

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