Scroll event for Meteor - javascript

I couldn't find a scroll event for meteor in the meteor docs. How do I go about doing something as someone scrolls the window down in a meteor application?
I've tried 'scroll window' : function(event) { ... } which doesn't work as expected.

I've been messing around with this as well.
I haven't found a way to do it cleanly within Template.template.events.
The obvious temporary solution right now would be using a simple jQuery scroll event.
$(window).scroll(function(){//your code}); should do the trick.
Things I was trying to use as the selector but to no avail were:
'scroll *'
'scroll body'
'scroll document'
and naturally
'scroll window'
I tried all of these selectors inside of a generic template's events, along with on UI.body's events, as that's the new blaze template that encompasses the page's body.
To reiterate: You're probably better off using jQuery for the time being.

This is a bit late but I came up with a solution; at least in the context of my current project.
I'm implementing D3 with Meteor, and I wanted a custom zoom functionality that changes the template's dimensions when the user scrolls.
Create a reactive variable 'zoom'
Template.graph.onCreated(function() {
var self = this;
self.zoom = new ReactiveVar(0);
$(window).on('scroll', function(e) {
// ... event processing stuff;
// say it produces value 'zoomAmount' ...
self.zoom.set(zoomAmount);
}
});
Create a helper that returns zoom.
Reference it in the template DOM in a hidden element to make it reactive.
Template.graph.helpers({
zoom: function() {
// This will be called when 'zoom' changes,
// so treat this as your events function
return Template.instance().zoom.get();
}
});

In Meteor there is no native template support for scroll events, so you have to do within your Template.name.onRendered callback. However, you will get a memory leak if you don't remove it from Template.name.onDestroyed. This is best accomplished with namespaced events, since something like $(window).off('scroll'); will detach all scroll events from window.
import { $ } from 'jquery';
Template.myTemplateName.onRendered(function(){
// You can do this multiple times
$(window).on('scroll.whateverNamespace', function() { ... });
$(window).on('scroll.whateverNamespace', function() { ... });
})
Template.myTemplateName.onDestroyed(function(){
$(window).off('scroll.whateverNamespace');
})

This is really late at this point, and I assume much has changed since the question was asked, but I came across this problem myself, and for anyone else that may need to know, the method that I found to work was to create a helper called 'scroll .container' where the container is a div that contains the main body of the page (where the user would scroll in my application) My function looked something like this :
Template.main_page.events({
'scroll .container': function(event) {
console.log(event.currentTarget.scrollTop);
}
});

As a partial solution, you can listen for the mousewheel event on whatever element you care about. A lot of times this is exactly what you want anyways.
As an example, the following event listener will prevent the user from scrolling with the scroll wheel at all, but they will still be able to use the navigation bar on the side of the page. (If you have not disabled it with overflowy: hidden;)
Template.body.events({
'mousewheel': function(event, template) {
console.log("scrolled");
return false;
}
});

Related

Disable then Re-Enable onClick()

I have a website that I am creating and there are different divs each with their own content. All of them are hidden except the main one that shows up on the homepage. The transitions are pretty long, and I like it that way, but the problem is that if somebody spams the navbar buttons it opens up all those divs ontop of each other. So to prevent that I want to temporarily disable the onClick for an <a></a> element. Then enable it after the transition is done. Currently I am able to disable it, but cannot find a way to re-enable it.
function disable(){
$(".bar").unbind();
$(".bar").removeAttr("onClick");
}
I know how to call a function after a certain amount of time, but what is the "enable" equivalent to the code in this function?
The exact opposite would be to set the onClick back on the element.
$('.bar').attr('onClick', function() { alert('blah'); });
or with vanilla js
document.querySelector(".bar")
.setAttribute('onClick', function() {...});
However, this is difficult to manage for many elements with the same functionality. It would be easier to have this entirely managed with javascript (and jQuery in this case).
function clickEvent(event) {
var self = $(this);
// Unbind the event
self.off(clickEvent);
// Click logic here
// Rebind event
self.on('click', clickEvent);
}
$('.bar').on('click', clickEvent);
Instead of disabling the event on the DOM, you can just add an extra piece of logic to your dynamic divs:
$('#mydiv').click(function() {
if(!inTransition())
// DO A THING
else
// DON'T DO A THING
});
As a side note: If you're doing a lot of dynamic DOM manipulation, you may want to look into using a data binding framework such as Angular or Knockout. jQuery is nice for simple DOM manipulations, but it can quickly become messy and hard to maintain if you're doing something complex (which it sounds like you are).
As somewhat of an extension to nmg49's answer, I'd like to provide a solution that's a little more in depth.
Essentially what you'll want to do is create a flag to determine whether or not you are currently transitioning, and cancel the onClick if it is true (disabling it after the transition is complete).
var isTransitioning = false;
$('.bar').onClick(function(){
if(isTransitioning) return;
isTransitioning = true;
// DO TRANSITION
});
Once the transition is complete, you simply set isTransitioning to false (either in a callback, or at the end of your onClick function; which ever one applies to your code).
This will ensure that, no matter how many times they click the button, they will not be able to transition if they're already in transition.

How do I unbind events properly when using allowSamePageTransition in jQuery Mobile?

I'm using the jQuery Mobile option allowSamePageTransition, which enables me to go from
page A > page A > page A ...
I need this to allow browsing through a catalogue of items. My problem is, the items need some form of interaction and I used to attach the interaction binding to document, because it is set before the elements affected are generated.
However, reloading the same page over and over again will re-bind my event handlers every time I reload.
My first idea was to use .off when the page is being hidden, but reloading a page #foo, will trigger pagehide on the same page being shown, so all bindings set on
$(document).on("pagebeforeshow.foo_events", "#foo", function(e) {
// bind when shown
});
will be unbound again by the previous #foo being hidden
$(document).on("pagehide", "#foo", function (e) {
$(this).off(".foo_events");
// removes bindings on #foo being hidden AND shown
});
The only solution I have come up with is plastering the document with classes, which I don't like doing:
priv.setBindings = function (param) {
var doc = $(document);
doc
.filter(function() { return $(this).is(".e_gallery") !== true; })
.on("pagebeforeshow.gallery", param.pageId, function (e) {
doc.addClass(".e_gallery");
// run stuff
});
};
But I'm no fan of attaching classes to the dom.
Question:
Is there a way to prevent multiple event bindings set on $(document) when going to the same page over and over again WITHOUT toggling classes?
Solution 1
Best solution would be to use pageinit to bind events. If you take a look at an official documentation you will find out that pageinit will trigger ONLY once, just like document ready, so there's no way events will be bound again. This is best solution because you don't have processing overhead like when removing events with off method.
Working jsFiddle example: http://jsfiddle.net/Gajotres/AAFH8/
Of course this will fail in case multiple HTML solution is used.
Solution 2
Remove event before you bind it:
$(document).on('pagebeforeshow', '#index', function(){
$(document).off('click', '#test-button').on('click', '#test-button',function(e) {
alert('Button click');
});
});
Working jsFiddle example: http://jsfiddle.net/Gajotres/K8YmG/
Solution 3
Use a jQuery Filter selector, like this:
$('#carousel div:Event(!click)').each(function(){
//If click is not bind to #carousel div do something
});
Because event filter is not a part of official jQuery framework it can be found here: http://www.codenothing.com/archives/2009/event-filter/
This is probably best solution because event is going to be bound ONLY once.
Solution 4
Probably an easiest of them all.
$(document).on('pagebeforeshow', '#index', function(){
$(document).on('click', '#test-button',function(e) {
if(e.handled !== true) // This will prevent event triggering more then once
{
alert('Clicked');
e.handled = true;
}
});
});
Working jsFiddle example: http://jsfiddle.net/Gajotres/Yerv9/
This is a 180 percent different solution then solution 3, in this case event is going to be bound numerous times but it will be allowed to execute only once.
More info
If you want to find more about this problem take a look at this article, working examples are included.

How to capture all scrolling events on a page without attaching an onscroll handler to every single container

Consider the following Web page:
<html>
<body onscroll="alert('body scroll event')">
<div style='width:200px;height:200px;overflow:auto' onscroll="alert('div scroll event')">
<div style='height:400px'>
</div>
</div>
</body>
</html>
This html creates a div with a scrollbar. If you move the scrollbar, the onscroll event on the div element is triggered. However, the onscroll event on the body is NOT fired. This is expected, since the W3C states that element onscroll events do not "bubble".
However, I'm developing a client-side web framework that needs to know any time a scroll bar on ANY element of the page is scrolled. This would be easy to do if onscroll bubbled, but unfortunately it does not. Is there any other way to detect onscroll events across an entire page? (Right now I'm focusing mainly on Webkit, so a Webkit-specific solution would be fine...)
Here are some things I've tried:
Capturing DOMAttrModified (doesn't seem to fire for moving scrollbars.)
Using DOM Observers (also don't seem to fire for scrollbars)
Changing the onscroll event type to bubble (seems to not be possible)
It seems the ONLY way to capture onscroll events globally is to attach an onscroll event to EVERY element that may scroll, which is very ugly and is going to hurt the performance of my framework.
Anyone know a better way?
The simplest way to detect all scroll events in modern browser would be using 'capturing' rather than 'bubbling' when attaching the event:
window.addEventListener('scroll', function(){ code goes here }, true)
Unfortunately as I am aware there is no equivalent in older browser such as <= IE8
I had this same issue.
The easiest way of course is to use jQuery. Be aware that this method could potentially slow down your page significantly. Also it will not account for any new elements that are added after the event is bound.
$("*").scroll(function(e) {
// Handle scroll event
});
In vanilla JavaScript, you can set the useCapture boolean to true on your addEventListener call, and it will fire on all elements, including those added dynamically.
document.addEventListener('scroll', function(e) {
// Handle scroll event
}, true);
Note though that this will fire before the scroll event actually happens. As I understand it, there's two phases events go through. The capture phase happens first, and starts from the page root (ownerDocument?) and traverses down to the element where the event happened. After this comes the bubbling phase, which traverses from the element back up to the root.
Some quick testing too showed that this may be how jQuery handles it (for tracking scrolls on all page elements at least), but I'm not 100% sure.
Here's a JSFiddle showing the vanilla JavaScript method http://jsfiddle.net/0qpq8pcf/
*...crickets chirping... *
OK, I guess this question isn't going to get any stackoverflow love, so I might as well answer my own question as to the best solution I've found so far, in case another user stumbles across this question:
The best solution I've come up with is to capture "onmousedown" and "onkeydown" for the BODY element: These events bubble, and so if a user tries to move a scrollbar on the page these global functions will fire as a by-product. Then, in these functions, simply look up event.target and attach a temporary "onscroll" event to those objects until the mouse/key is "up" again. Using that method, you can avoid "handler bloat" and still globally capture all "onscroll" events. (I think this will work for "mouse wheel" scrolling as well, but my research on that final wrinkle is still pending.)
The following works fine when you want to i.e. close a dialog after anything in the background is scrolled:
var scrollListener = function(e) {
// TODO: hide dialog
document.removeEventListener('scroll', scrollListener, true);
};
document.addEventListener('scroll', scrollListener, true);
I needed to handle scrolling in any context in a complex of custom elements with scroll events in shadowRoots. This covers at least part of the problem in my scenario and generally borrows from the answers and comments here in the context of these newer web component APIs. Attaching and detaching the listener in the appropriate lifecycle callbacks works well so-far (once might not fit your use-case).
self.addEventListener('mousewheel', handler, {capture: true, once: true});
self.addEventListener('keydown', handler, {capture: true, once: true});
Note too the event.composedPath() provides the entire event path through all the shadowRoots with all the nodes if specifics about the scrolling context are needed. If this is the case it might make sense to use this approach and attach a new handler for that specific scenario--to the node of interest.
Like drcode said, capture on body tag is the trick. I just add touchmove to work on mobile.
document
.querySelector("body")
.addEventListener("mousewheel", e => {
console.log("scroll");
});
document
.querySelector("body")
.addEventListener("touchmove", e => {
console.log("scroll");
});
Regards,

Run a script when div is inserted

I have a script that does graphing, using jqplot. It works fine when the document is loaded rendering each graph using jquery's .each method. However, the problem lies when I replace the div with another one when a bar is clicked. It is suppose to render another graph in the position of the old graph. It changes the graph but does not execute the script.
The script that loads the items has this function to change all divs to graphs:
$("div.barchart").each(function(){
barChart($(this).attr("id"),$(this).attr("data-xmlurl"));
});
is there another way to do this so that it would work when a div is changed too?
Update:
Rails generates a script that is ran. However, it doesn't seem to work when I have this:
chart$=$("#<%=params[:chart_id]%>");
chart$.replaceWith("<%=escape_javascript(render :partial=>"chart_partial"}%>");
barChart(chart$.get(0).attr("id"),chart$.get(0).attr("data-xmlurl"));
Note:
For reference, the actual source code can be found in the jquery_cheats project
Perhaps you could add a listener on the parent element? Is it OK if the barChart() function gets called more than once?
Maybe something like this:
$("div.barchart").parent().on("DOMSubtreeModified", function(e) {
// (or maybe use DOMNodeInserted event instead)
$("div.barchart[id][data-xmlurl]").each(function() {
barChart($(this).attr("id"),$(this).attr("data-xmlurl"));
});
});
You can check out my jsFiddle for this here.
On the current application I'm working on, I'm stuck with version 1.5.2. To get around this, I would unbind and rebind my event and load the initialization in both "ajaxComplete" and "ready". I wasn't able to get the DOM to automatically rebind the event. Delegate is suppose to work like "on", but in my instance I still had to use the below logic.
In short, it would look something like this.
$(document).ready(function () {
InitSomethingCool();
});
$(document).ajaxComplete(function() {
InitSomethingCool();
});
function InitSomethingCool(){
$(".something").unbind('click').click(function(e) {
//Unbind and rebind click event.
alert('You clicked me!');
});
}
Reference:
http://api.jquery.com/on/
http://api.jquery.com/delegate/

jquery/javascript: function(e){.... what is e? why is it needed? what does it actually do/accomplish?

$('#myTable').click(function(e) {
var clicked = $(e.target);
clicked.css('background', 'red');
});
Can someone explain this to me, and explain why e is needed, and what it actually does..
Using e is just a short for event. You can pass any variable name you desire.
// would work just the same
$('#myTable').click(function(anyothername) {
var clicked = $(anyothername.target);
});
You can check out more on jQuery's handling of events.
One benefit to having e (the object that raised the event) allows you to prevent the propagation of default behaviors for certain elements. For example:
<a id="navLink" href="http://mysite/someOtherPage.htm">Click For Info</a>
renders a link that the user can click. If a user has JavaScript disabled (why? I dunno), you want the user to navigate to someOtherPage.htm when they click the link. But if they have JavaScript enabled, then you want to display a modal dialog and not navigate away from the page. You would handle this by preventing the default behavior of the anchor/link and displaying the modal as such:
$("#navLink").click(function(e) {
e.preventDefault(); //this prevents the user from navigating to the someOtherPage.htm
$("#hiddenDiv").dialog({
//options
}); //show the dialog
});
So having that parameter available allows you to, among other things described in other answers, prevent the default behavior of the selected element.
Hope this helps!
I'm speaking in theory as to I'm no expert but I achieved the desired result by using he the little (e) which doesn't have to be an e lol
I figured it out. It's a way of passing the same event from one function to another.
In simpler terms. I wanted to make the page navigation an elastic scroll function, however, I wanted the page to navigate by hover "and" I wanted the same navigation to be clickable upon certain conditions. I also wanted the same dynamic navigation from other click events that were not links. To keep the current target and still use the navigation function I had to set the little (e) because jQuery will lose the scope of $(this) as the same target of the function lol. Here's a quick example.
function navigate_to_page(e){
var target = $(e.currentTarget).attr('href'); //--This is the same as $(this) but more static to bring out of it's scope
$('html, body').animate({
'scrollTop':$(target).offset().top-0,
'scrollLeft': $(target).offset().left-$(window).width()*0.0}, 2000, 'easeOutBounce');
}
Don't let the gibberish confuse you. It's just a simple page scroll animation. The thing to pay attention to is the e.currentTarget. e is our variable and currentTarget is a jQuery equivalent to $(this) so those together is a Globular $(this) function.
Now I call it by another function with condistions like so
$('#myNavigationDiv a').on('mouseenter', function(e){
if($(myCondition) === true){
return false;
}else{
navigate_to_page(e);
}
});
See how the little (e) linked everything together?
Now you can substitute (e) to (whateveryouwant). By calling e in both functions it matched e.currentTarget and you can apply this to whatever detailed specific functions you need and save yourself LITERALLY pages of code lol
It's the formal parameter for the function. jQuery will pass in an event object when the function is called. This is used to determine the target. As noted in the documentation, jQuery will always pass an event object even when the browser (e.g. IE) doesn't.
In this case, the target tells you which element was originally clicked.

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