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can't change z index with javascript

I'm trying to change the Z index of an image according to the scroll position,currently in chrome (but it should be working on all broswers).
anyway, it's not working on chrome, unless I get into inspection mode and I don't understand why it's only working in inspection mode?
this is the script:
$( window ).scroll(function() {
var scrollTop = $(window).scrollTop();
if ($(this).scrollTop()>700) {
document.getElementById("back-ground-image").style.zIndex = "-9";
console.log("-9");
} else {
document.getElementById("back-ground-image").style.zIndex = "-19";
console.log("-19");
}
});

Problem
What you need is $(document) not $(window).
By default, you scroll the $(document), not the $(window).
However, when you open your Chrome DevTools, the $(window) is not being scrolled which is why your code works.
To fix the issue, change $(window).scroll() to $(document).scroll() and $(window).scrollTop() to $(document).scrollTop()
Improvements
1. Use jQuery functions
Also, if you're already using jQuery, why not use jQuery selectors and .css():
$("#back-ground-image").css('zIndex', '-9')
instead of
document.getElementById("back-ground-image").style.zIndex = "-9";
2. Use DRY code
(Don't Repeat Yourself)
If you follow recommendation #1, why not set $("#back-ground-image") to a variable instead of repeating it twice.
$(document).scroll(function() {
var scrollTop = $(document).scrollTop(),
$bkImg = $("#back-ground-image");
if ($(this).scrollTop() > 700) {
$bkImg.css('zIndex', '-9');
console.log("-9");
} else {
$bkImg.css('zIndex', '-19');
console.log("-19");
}
});
Otherwise, you could use:
$(document).scroll(function() {
var scrollTop = $(document).scrollTop(),
background = document.getElementById("back-ground-image");
if ($(this).scrollTop()>700) {
background.style.zIndex = "-9";
console.log("-9");
} else {
background.style.zIndex = "-19";
console.log("-19");
}
});

Run function() if appear in viewport ? jquery-viewport-checker

I use anime-js for create an animation. But, It is far in the page. I would like to launch my animation function when the section in which the item to be animated appears on the screen.
I tried a plugin that I like to use (jquery viewportchecker) but it does not seem to do that.
Can you help me ?
Thank you

I found a solution. The problem with your method is that the function repeats itself to infinity.
I create a little function for check if element is visible. With that, no plugin needed.
function checkVisible( elm, evale ) {
var evale;
evale = evale || "object visible";
var viewportHeight = $(window).height(), // Viewport Height
scrolltop = $(window).scrollTop(), // Scroll Top
y = $(elm).offset().top,
elementHeight = $(elm).height();
if (evale == "object visible") return ((y < (viewportHeight + scrolltop)) && (y > (scrolltop - elementHeight)));
if (evale == "above") return ((y < (viewportHeight + scrolltop)));
}
I also created a variable var counter = 0;. And as soon as the function is called, I increment by 1.
$(window).on('scroll',function() {
if (counter == 0){
if (checkVisible($('.frontend'))) {
// Your function here
}
}
}
At the first time the function will be called, counter will be 1, and thus, the function will not repeat. Thank you for your help !

jQuery.appear
This plugin implements custom appear/disappear events which are fired when an element became visible/invisible in the browser viewport.
https://github.com/morr/jquery.appear
$('someselector').on('appear', function(event, $all_appeared_elements) {
// this element is now inside browser viewport
});
$('someselector').on('disappear', function(event, $all_disappeared_elements) {
// this element is now outside browser viewport
});
Also this plugin provides custom jQuery filter for manual checking element appearance.
$('someselector').is(':appeared')

Have you tried using JQuery's on load method?
Something like
$(document).on('load', '.exampleClass', function() { //do stuff } )

Toggle class when object visible in the viewport

I need a script which toggle a class when another class or section is visible in the viewport (during scrolling).
Here I have an script which works for precised distance from top, but can somebody help me to modify it for my needs?
$(window).scroll(function(){
if ($(this).scrollTop() > 50) {
$('#viewport').addClass('turn_on');
} else {
$('#viewport').removeClass('turn_on');
}
});

A couple of things. First the scroll event (as well as the resize event) fire multiple times. Traditionally, developers have used something called debouncing to limit the number of times a function fires. I've never got it to work correctly, so instead I check if a condition is met before continuing. You are basically doing this already.
var bool = false
$(window).on('scroll', function(){
if(!bool){
bool = true;
//fire the function and then turn bool back to false.
};
});
The next thing you need is to identify the element to add the class to. Let's say it has an id of foo.
var yOffset = $('#foo').offset().top;
From here, you'll need to compare the current vertical scroll position with that of the yOffset. You may also need to add the height of the element for when it scrolls out of frame.
var elHeight = $('#foo').height();
The element should be completely in frame with the $(window).scrollTop() equals the yOffset and out of frame when the $(window).scrollTop() is greater than yOffset + elHeight.
This is all assuming the element isn't in the frame to begin with. If it is, it will be trickier but it's a start.

Working fiddle
Try to add function that detect if element passed in argument is visible :
function isVisisble(elem){
return $(elem).offset().top - $(window).scrollTop() < $(elem).height() ;
}
$(window).scroll(function(){
if (isVisisble( $('your_element') ))
$('#viewport').addClass('turn_on');
} else {
$('#viewport').removeClass('turn_on');
}
});
Hope this helps.

Thx everyone for help.
Here I found the solution: LINK
And here is the modified script:
$(document).ready(function () {
var windowHeight = $(window).height(),
gridTop = windowHeight * 0.1,
gridBottom = windowHeight * 1;
$(window).on('scroll', function () {
$('.inner').each(function () {
var thisTop = $(this).offset().top - $(window).scrollTop();
if (thisTop > gridTop && (thisTop + $(this).height()) < gridBottom) {
$(this).addClass('on');
}
});
});
});

jQuery scroll event switching back and forth between if/else

I have a column that I want to stick to the top of the page, but once it gets to the point of sticking any further scrolling causes it to jump back and forth between having the added class and not.
function sticky_relocate() {
var window_top = $(window).scrollTop();
var div_top = $('#stick-me').offset().top;
if (window_top >= div_top) {
$('#stick-me').addClass('stick');
} else {
$('#stick-me').removeClass('stick');
}
}
$(function () {
$(window).scroll(sticky_relocate);
sticky_relocate();
});
My intuition tells me it's an issue with the conditional statements, but I'm not sure how else I can structure it. Thanks in advance!

You don't need to add/remove the class as such, simply toggle class. Without seeing your CSS and other JS conflicts all I can do is show you a working example.
DEMO http://jsfiddle.net/tbdbyxvu/
var $window = $(window),
$stickyEl = $('#the-sticky-div'),
elTop = $stickyEl.offset().top;
$window.scroll(function() {
$stickyEl.toggleClass('sticky', $window.scrollTop() > elTop);
});

the #stick-me element is getting moved when your class 'stick' is applied (as you would want).
When your function runs a second time, div_top is now a new (larger) number and your if statement (which proved true the first time) now proves false and removes the class.
In short, your class is being added and removed over and over again.
I would suggest storing #stick-me's original location on page load in a variable startingPoint outside of sticky_relocate, then adding/removing the class when scrollTop is greater than startingPoint.
function sticky_relocate() {
var window_top = $(window).scrollTop();
if (window_top >= startingPoint) {
$('#stick-me').addClass('stick');
} else {
$('#stick-me').removeClass('stick');
}
}
$(function () {
var startingPoint = $('#stick-me').offset().top;
$(window).scroll(sticky_relocate);
});

javascript: detect scroll end

I have a div layer with overflow set to scroll.
When scrolled to the bottom of the div, I wanna run a function.

The accepted answer was fundamentally flawed, it has since been deleted. The correct answer is:
function scrolled(e) {
if (myDiv.offsetHeight + myDiv.scrollTop >= myDiv.scrollHeight) {
scrolledToBottom(e);
}
}
Tested this in Firefox, Chrome and Opera. It works.

I could not get either of the above answers to work so here is a third option that works for me! (This is used with jQuery)
if (($(window).innerHeight() + $(window).scrollTop()) >= $("body").height()) {
//do stuff
}
Hope this helps anyone!

if ((window.innerHeight + window.scrollY) >= document.body.offsetHeight)
{
//your code here
}
I too searched it and even after checking all comments here and more,
this is the solution to check if reached the bottom or not.

OK Here is a Good And Proper Solution
You have a Div call with an id="myDiv"
so the function goes.
function GetScrollerEndPoint()
{
var scrollHeight = $("#myDiv").prop('scrollHeight');
var divHeight = $("#myDiv").height();
var scrollerEndPoint = scrollHeight - divHeight;
var divScrollerTop = $("#myDiv").scrollTop();
if(divScrollerTop === scrollerEndPoint)
{
//Your Code
//The Div scroller has reached the bottom
}
}

This worked for me:
$(window).scroll(function() {
buffer = 40 // # of pixels from bottom of scroll to fire your function. Can be 0
if ($(".myDiv").prop('scrollHeight') - $(".myDiv").scrollTop() <= $(".myDiv").height() + buffer ) {
doThing();
}
});
Must use jQuery 1.6 or higher

I found an alternative that works.
None of these answers worked for me (currently testing in FireFox 22.0), and after a lot of research I found, what seems to be, a much cleaner and straight forward solution.
Implemented solution:
function IsScrollbarAtBottom() {
var documentHeight = $(document).height();
var scrollDifference = $(window).height() + $(window).scrollTop();
return (documentHeight == scrollDifference);
}
Resource: http://jquery.10927.n7.nabble.com/How-can-we-find-out-scrollbar-position-has-reached-at-the-bottom-in-js-td145336.html
Regards

I created a event based solution based on Bjorn Tipling's answer:
(function(doc){
'use strict';
window.onscroll = function (event) {
if (isEndOfElement(doc.body)){
sendNewEvent('end-of-page-reached');
}
};
function isEndOfElement(element){
//visible height + pixel scrolled = total height
return element.offsetHeight + element.scrollTop >= element.scrollHeight;
}
function sendNewEvent(eventName){
var event = doc.createEvent('Event');
event.initEvent(eventName, true, true);
doc.dispatchEvent(event);
}
}(document));
And you use the event like this:
document.addEventListener('end-of-page-reached', function(){
console.log('you reached the end of the page');
});
BTW: you need to add this CSS for javascript to know how long the page is
html, body {
height: 100%;
}
Demo: http://plnkr.co/edit/CCokKfB16iWIMddtWjPC?p=preview

This will actually be the correct answer:
function scrolled(event) {
const container = event.target.body
const {clientHeight, scrollHeight, scrollY: scrollTop} = container
if (clientHeight + scrollY >= scrollHeight) {
scrolledToBottom(event);
}
}
The reason for using the event is up-to-date data, if you'll use a direct reference to the div you'll get outdated scrollY and will fail to detect the position correctly.
additional way is to wrap it in a setTimeout and wait till the data updates.

Take a look at this example: MDN Element.scrollHeight
I recommend that check out this example: stackoverflow.com/a/24815216... which implements a cross-browser handling for the scroll action.
You may use the following snippet:
//attaches the "scroll" event
$(window).scroll(function (e) {
var target = e.currentTarget,
scrollTop = target.scrollTop || window.pageYOffset,
scrollHeight = target.scrollHeight || document.body.scrollHeight;
if (scrollHeight - scrollTop === $(target).innerHeight()) {
console.log("► End of scroll");
}
});

Since innerHeight doesn't work in some old IE versions, clientHeight can be used:
$(window).scroll(function (e){
var body = document.body;
//alert (body.clientHeight);
var scrollTop = this.pageYOffset || body.scrollTop;
if (body.scrollHeight - scrollTop === parseFloat(body.clientHeight)) {
loadMoreNews();
}
});

To do the same in React/JSX, here is the snippet.
export const scrolledToEnd = event => {
const container = event.target;
if (container.offsetHeight + container.scrollTop >= container.scrollHeight) {
return true;
}
return false;
};
And in your component add
<Component onScroll={scrolledToEnd}>

There is experimental onscrollend event https://developer.mozilla.org/en-US/docs/Web/API/Document/scrollend_event
For now works only in firefox 109+, if other browsers catch up will be very nice.
Have polyfill for that https://github.com/argyleink/scrollyfills
Use like
import "scrollyfills";
...
scrollContainer.addEventListener(
"scrollend",
(ev) => { console.log('scroll END') }
);

I found this methode to get the end of the scroll :
let TheBody = document.getElementsByTagName("body"); // I choose the "body" element for my exemple
function OnScrolling(){ // put this on a scrolling EVENT
let ScrollEnd = TheBody[0].scrollHeight - window.innerHeight; // this is the scroll end Pixel
if (ScrollEnd.toFixed() == window.scrollY.toFixed()){
//do stuff
}
}

Okay now for your DIV or any other element that have a scrolling I found this method on JavaScript :
let D = document.getElementById("D1"); // I gave "D1" as id to my div
// this one is to calculate the scroll end Pixels
let Calc = D.scrollHeight - D.clientHeight;
function ScrollingInD1() {
//this one is to calculate the scrolling percent while going through the <div> it can help for "Responsivity"
let percent = (D.scrollTop * 100) / Calc;
if (D.scrollTop == Calc) {
// do Stuffs
}
}