Remove scroll function upon window resize/media query - javascript

I have a navigation menu set to display:none, which appears upon scroll and disappears once back at the top.
Is there a way to disable the scroll function once I reach a certain breakpoint (ex. max-width: 786px) and display the menu?
Javascript
$(window).on("scroll", function() {
if($(window).scrollTop()) {
$('nav').addClass('show');
}
else {
$('nav').removeClass('show');
}
})
CSS
.show {
display: block
}

You can solve this using either javascript or CSS, however I would personally go with the javascript one.
First up, for a javascript solution, the function you need is:
window.innerWidth
It will return the entire window width not including scroll bars. Read more about it here.
So, as Temani Afif suggested, you would write a test inside your scroll function to check for the desired window width like so:
$(window).on("scroll", function() {
if (window.innerWidth <= 786) return;
// Your other code here
})
For a purely CSS solution, you could override the effect of the 'show' class with a media query:
.show {
display: block
}
#media screen and (max-width: 786px) {
nav {
display: block !important
}
}
More on media queries here

You can activate/deactivate the scroll listener on browser resize. This way your scroll listener wont be called everytime user scrolls when browser width is more than 786px.
var scrollListenerActive = false;
var handleScrollListener = function() {
if( $(window).width() < 786 && !scrollListenerActive ) {
$(window).on("scroll", function() {
if($(window).scrollTop()) {
$('nav').addClass('show');
}
else {
$('nav').removeClass('show');
}
});
scrollListenerActive = true;
} else {
$(window).off("scroll");
scrollListenerActive = false;
}
}
$(document).ready(handleScrollListener); // attach the listener on page load
$(window).resize(handleScrollListener); // attach/remove listener on window resize

That's a good strategy above, however the event you want to listen for is simply 'resize', on the window object (some older browsers can do it on any dom element, but better to be consistent and current with the standard).
So something like:
window.addEventListener('resize',function(){
if(window.innerWidth >= 768){
document.body.style['overflow-x'] = 'hidden';
}
else{
document.body.style['overflow-x'] = 'auto';
}
});
You can trade 'auto' for 'scroll' if you want the scrollbar to always show when less than 768.
Similarly, you can switch out 'overflow' instead of 'overflow-x' if you want to affect both scrollbars.
Keep in mind that the event tends to fire for every width and height change as the window is resized, in case you have other logic that might have an issue with firing many times (thousands or more) as it is resized.
This also works on maximize/restore, as they trigger the resize event as well.
Here's MDN's doc on the resize event if needed:
https://developer.mozilla.org/en-US/docs/Web/Events/resize
This is vanilla javascript, so it should work whether you're using a lib like jquery or not.

Related

Issue to fire scroll events with Smooth Scrollbar plugin

I'm using the plugin Smooth Scrollbar (here).
I have an animation on my fixed header (outside the smooth scrollbar container) and triggered when user starts scrolling the smooth scrollbar container. As mentioned in the documentation (here), it's not possible that scrollbars fire scroll events. So we have to use:
scrollbar.addListener((status) => {
...
});
This is the code to animate my fixed header:
$(window).scroll(function() {
if ($(this).scrollTop() > 50){
$('.site_header').removeClass('is--large').addClass('is--small');
}
else{
$('.site_header').removeClass('is--small').addClass('is--large');
}
});
I can't figure it out how to integrate it with Smooth Scrollbar plugin. I tried various solutions to use addListener but I can't make it work.
Any help would be much appreciated!
I know it's been a while but:
const scroller = document.querySelector('.scrollable');
const bodyScrollBar = Scrollbar.init(scroller, { damping: 0.1, delegateTo: window, alwaysShowTracks: false });
bodyScrollBar.addListener( () => {
if (bodyScrollBar.scrollTop > 50){
$('.site_header').removeClass('is--large').addClass('is--small');
}
else{
$('.site_header').removeClass('is--small').addClass('is--large');
}
}
)
where .scroller is my scrolling container. Whenever you call the variable bodyScroller in the console you can see all options set and what value you can retrieve at any time. In this instance, by calling .scrollTop (NOT a function) you can retrieve its offset top value at any time.

Limiting Scroll and Resize events

This is a general question about a problem I run into often, where I need something to happen at a certain screen width, or scrollTop position, so I end up triggering events for the entire scroll or resize event. This seems really unnecessary and hurts performance. I am wondering what steps I can take to limit calling code written inside scroll or resize events so that I am only triggering these events when I need them.
In the example below I just want the background color to change at a certain scrollTop offset, but since its wrapped in a scroll event, it gets trigged for every pixel.
I know there are things like lodash, but wouldn't I have the same problem of a throttle running just as often on scroll? Any general approach help would be greatly appreciated.
$(window).on('scroll', function() {
var scrollPosition = $(window).scrollTop();
if (scrollPosition > 500) {
$('.container').css('background-color', 'blue');
} else {
$('.container').css('background-color', 'red');
}
});
.container {
background-color: red;
height: 2000px;
width: 100%;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="container">
</div>
You should really have a look at Intersection Observer (IO), this was created to solve problems like you described.
With IO you tell the browsers which elements to watch and the browser will then execute a callback function once they come into view (or leave the view) or intersect with each other.
First you have to set the options for your observer:
let options = {
rootMargin: '0px',
threshold: 1.0
}
let observer = new IntersectionObserver(callback, options);
Here for example I specified that everytime the observed element is fully visible in viewport I want to execute a callback function. Obviously you can set the parameters to your liking.
Second you have to specify which elements you want to observe:
let target = document.querySelectorAll('.container');
observer.observe(target);
Here I say I want to watch all elements on the page with the class container.
Last I have define the callback function which will be triggered everytime one container element is visible.
let callback = (entries, observer) => {
entries.forEach(entry => {
// Each entry describes an intersection change for one observed
// target element
});
};
With this approach you don't have to worry about performance issues of scroll events.
Since you can theoretically build all of this with listening to scroll events too you can also use this official polyfill from w3c to support older browsers.
You can also stop observing an element if you don't want to observe it anymore.
Lastly have a look at this demo, it shows you can easily change the background-color of an element depending on how much of the element is visible.
You definitely should use throttle or debounce for scroll or resize handlers. It can be lodash or your own implementation. Cancelled handler triggering costs almost nothing in term of performance, so don't even bother about that.
You can use a library like Waypoint.js to accomplish a similar feature. You'll just need to add an element at the event position and it should work quite efficient. Otherwise there aren't that many other ways except the ones that Huangism already mentioned. As you also asked about resizing events it may be better to use CSS media rules because these are quite performant and easy to use:
#media only screen and (max-width: 600px) {
.container {
background-color: blue;
}
}
As mentioned in comments, you just need to throttle the action. Here is a sample code of how scrolling throttling would work
The expensive part of the scroll/resize event is the part where you are doing something, like when you getting the scrolltop and comparing it then running something. By throttling, your executable code don't actually run until the threshold is reached which saves you big time on performance
Resizing would be the same except you do it for the resize function of course
scrollTimer = setTimeout(function() {
// your execution code goes here
}, 50);
var scrollInit = false;
var scrollTimer = null;
if (!scrollInit) {
var waiting = false;
$(window).on("scroll", function(event) {
if (waiting) {
return false;
}
clearTimeout(scrollTimer);
waiting = true;
scrollTimer = setTimeout(function() {
console.log("scroll event triggered");
}, 50);
});
}
scrollInit = true;
div {
background: grey;
height: 2000px;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div></div>

Bind function to custom condition

Note: I rarely use JS and jQuery so please excuse if the question is odd.
I am trying to add a div to my page (to a menu specifically) but only if the page is smaller than a certain width. Basically I need an event handler that allows me to wait for that condition to be met and run a function once it is (similar to how you would do with on.("click")) but I have no idea how to accomplish that.
Any help would be greatly appreciated!
have a look at the following code:
var $myDiv = $("<div class='myDiv'></div>");
$(window).resize(function () {
var windowWidth = $(this).width();
if (windowWidth < 200) {
$("body").append($myDiv);
} else {
$myDiv.remove();
}
});
we monitor the window resize event, and append/remove the div as per your condition.
Live Example
play around with the bottom right side of the fiddle (the result pane) and resize it to see what happens.
This is without the event handler, but you can add it in a resize event handler:
if (window.matchMedia("(min-width:700px)").matches) {
// viewport width is at least 700px
} else {
// viewport is smaller than 700px
}

iOS 8 glitch effecting window resize

I've got some very simple code:
$(function() {
$(window).resize(function () {
if ($(window).width() < 500) {
$("#foo").show(); $("#foo2").hide();
} else if ($(window).width() > 501) {
$("#foo2").show(); $("#foo").hide();
}
}).resize();
});
All was working fine on desktop (all major browsers) and mobile (as many as I could test), till iOS 8 came out. Now when a users scrolls in Safari the javascript falls back to 'else if', creating 'foo2' and hiding 'foo' despite the browser not resizing. This is for a menu, as such the menu closes if the user scrolls which shouldn't be happening.
If I remove the window resize function all works as it should, however the menu doesn't update in real time if the user resizes the browser window.
Is there an alternative to window resize I can use to achieve the same effect?
...so, considering I get the problem as you describe it, you can avoid javascript and do it using pure css and media queries:
#media (max-width:500px) {
#foo {
display:block;
}
#foo2 {
display:none;
}
}
#media (min-width:501px) {
#foo2 {
display:block;
}
#foo {
display:none;
}
}
edit: ..this will definately have nothing to do with scrolling and will certainly be faster and cleaner
This might be a little late, but I'd store the width of the window on load and then check against that on the resize to ensure an actual resize took place horizontally. That would ensure that the code only fired when the browser changed size on the x axis.
var windowWidth = $(window).width();
$(window).resize(function(){
if (windowWidth !== $(window).width())
{
windowWidth = $(window).width();
// rest of your code goes here
}
});
Remember that the resize event could fire quite a lot while someone is resizing, so you may want to limit the whole thing using setInterval, but that's a separate discussion.

Jquery, Remove class when width screen is 1050px

This is the JS code i'm using:
$("document").ready(function($){
var nav = $('#menu2');
$(window).scroll(function () {
if ($(this).scrollTop() > 90) {
nav.addClass("f-nav");
} else {
nav.removeClass("f-nav");
}
});
But i can't seem to get this into my code.
function checkWidth(init){
/*If browser resized, check width again */
if ($(window).width() < 514) {
$('html').addClass('mobile');
}
else {
if (!init) {
$('html').removeClass('mobile');
}}}$(document).ready(function() {
checkWidth(true);
$(window).resize(function() {
checkWidth(false);
});
And what i want is that when .f-nav is added to #menu2, when the screen is <1050 the classshould be removed.
To change html to #menu2, just replace one with the other. jQuery is pretty simple in this respect
if ($(window).width() < 514) {
$('#menu2').addClass('f-nav');
} else {
$('#menu2').removeClass('f-nav');
}
JSFiddle
There are a few ways to do that:
Javascript only
See it in action: Fiddle
$(window).resize(function() {
if ($(window).width() < 1050) {
$selector.removeClass('my-class');
} else {
$selector.addClass('my-class');
}
}).resize(); // trigger resize event initially
And don't forget: You don't have to place $(window).resize inside $(document).ready.
Mixed Javascript & CSS
See it in action: Fiddle
This technique is explained here: http://www.senaeh.de/media-query-variablen-javascript-auslesen/
Basic principle: set a variable with a CSS pseudo element and get it with javascript.
This workaround is good if you have to use Javascript even if media queries are used, because you don't have to declare the breakpoint twice.
CSS
#media screen and (max-width: 1050px) {
body:after {
content: 'tablet';
display: none;
}
}
Javascript
var mode = window.getComputedStyle(document.body,':after').getPropertyValue('content');
Be aware: IE < 9 doesn't support getComputedStyle. You have to use a polyfill like this one.
this is best achieved with a media query
#media screen and (max-width:1050px){
.mobile{
/* will only apply on devices narrower than 1050px */
}
}
EDIT: also possible to use media queries with javascript in modern browsers
if (matchMedia) { // check if browser supports media queries from JavaScript
var mq = window.matchMedia("(max-width: 1050px)");
WidthChange(mq);
// every time width changes, check the media query
mq.addListener(function WidthChange(mq){
if(mq.matches){
//we are in a mobile size browser
$('#menu2').addClass('mobile');
$('#menu2').removeClass('f-nav');
} else{
// desktop browser
$('#menu2').addClass('f-nav');
$('#menu2').removeClass('mobile');
}
});
}
When you load a website on a screen bigger than your breakpoint, the script wont work, because you need to re-calculate the screen size(refresh the page in this case). You need to get the width of the screen on resize. Use resize() method, and inside it place your test condition, and assign the class to your element. Reference to help you: http://api.jquery.com/resize/
If you want to change the class of a div in JS, you can do something like that:
document.getElementById("#YourId").className = "YourNewClass"
It will just change your class attribute :-)
Like that, you can also check which class is used and do what you want to do with that.
Edit thanks to Olaf Dietsche: this must be a duplicated post, here can be your answer: jquery, add/remove class when window width changes

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