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scrollTop() is not working in mobile view or mobile devices

I want to scroll to the bottom of the div when the page loads. I am using jQuery's animate() function this. The issue is that my code is working on desktop view, but if I change it to mobile view then my code is not working.
$(".chat-msg-list").animate({
scrollTop: $(".chat-msg-list").prop("scrollHeight")
}, 1000);

jQuery:
$(".chat-msg-list").animate({
scrollTop: $(".chat-msg-list").offset().top},
}, 1000);
Javascript:
function getElementY(query) {
return window.pageYOffset + document.querySelector(query).getBoundingClientRect().top
}
function doScrolling(element, duration) {
var startingY = window.pageYOffset
var elementY = getElementY(element)
// If element is close to page's bottom then window will scroll only to some position above the element.
var targetY = document.body.scrollHeight - elementY < window.innerHeight ? document.body.scrollHeight - window.innerHeight : elementY
var diff = targetY - startingY
// Easing function: easeInOutCubic
// From: https://gist.github.com/gre/1650294
var easing = function (t) { return t<.5 ? 4*t*t*t : (t-1)*(2*t-2)*(2*t-2)+1 }
var start
if (!diff) return
// Bootstrap our animation - it will get called right before next frame shall be rendered.
window.requestAnimationFrame(function step(timestamp) {
if (!start) start = timestamp
// Elapsed miliseconds since start of scrolling.
var time = timestamp - start
// Get percent of completion in range [0, 1].
var percent = Math.min(time / duration, 1)
// Apply the easing.
// It can cause bad-looking slow frames in browser performance tool, so be careful.
percent = easing(percent)
window.scrollTo(0, startingY + diff * percent)
// Proceed with animation as long as we wanted it to.
if (time < duration) {
window.requestAnimationFrame(step)
}
})
}
//Apply event handlers. Example of firing the scrolling mechanism.
doScrolling('#section1', 1000)

Smooth scrolling on mouse wheel?

Instead of the normal mouse scroll speed, I'd like to make it slower and smoother and as consistent as it can in modern browsers.
I have already tried using a few plugins like NiceScroll (https://nicescroll.areaaperta.com/).
But after installing it, for some reason it puts an overflow: hidden; on my content and can't scroll anywhere after. I don't need any custom-designed scrollbars. I just need the scrolling to be smoother when using the mouse scroll or vertical scroll bar like this:
http://pervolo.com/
Would anyone please enlighten me about this? I plan to use the skrollr plugin (https://github.com/Prinzhorn/skrollr) along with the smooth scrolling.

This may get you going:
$(window).on('mousewheel DOMMouseScroll', function(e) {
var dir,
amt = 100;
e.preventDefault();
if(e.type === 'mousewheel') {
dir = e.originalEvent.wheelDelta > 0 ? '-=' : '+=';
}
else {
dir = e.originalEvent.detail < 0 ? '-=' : '+=';
}
$('html, body').stop().animate({
scrollTop: dir + amt
},500, 'linear');
})
DOMMouseScroll and e.originalEvent.detail are required for Firefox. Change amt to be your desired scroll distance, and change 500 to be your desired scroll speed.
Fiddle: http://jsfiddle.net/utcsdyp1/1

I succeeded in making the scroll by mouse wheel look smooth as butter! Copy-paste the following snippet and try yourself.
let easeInOutQuint = t => t<.5 ? 16*t*t*t*t*t : 1+16*(--t)*t*t*t*t; // Easing function found at https://gist.github.com/gre/1650294
// With this attempt I tried to make the scroll by mouse wheel look smooth
let delay = ms => new Promise(res => setTimeout(res, ms));
let dy = 0;
window.addEventListener("wheel", async e => {
// Prevent the default way to scroll the page
e.preventDefault();
dy += e.deltaY;
let _dy = dy; // Store the value of "dy"
await delay(150); // Wait for .15s
// If the value hasn't changed during the delay, then scroll to "start + dy"
if (_dy === dy) {
let start = window.scrollY || window.pageYOffset;
customScrollTo(start + dy, 600, easeInOutQuint);
dy = 0;
}
}, { passive: false });
function customScrollTo(to, duration, easingFunction) {
let start = window.scrollY || window.pageYOffset;
let time = Date.now();
let timeElapsed = 0;
let speed = (to - start) / duration;
(function move() {
if (timeElapsed > duration) {
return;
}
timeElapsed = Date.now() - time;
// Get the displacement of "y"
let dy = speed * timeElapsed;
let y = start + dy;
// Map "y" into a range from 0 to 1
let _y = (y - start) / (to - start);
// Fit "_y" into a curve given by "easingFunction"
_y = easingFunction(_y);
// Expand "_y" into the original range
y = start + (to - start) * _y;
window.scrollTo(0, y);
window.requestAnimationFrame(move);
})();
}

You can catch an action when user scrolls using $(element).on( "scroll", handler ), then, using, for example this code
$('html, body').animate({
scrollTop: $("#target-element").offset().top
}, 1000);
scroll to some element using jQuery

Scroll smoothly to specific element on page

I want to have 4 buttons/links on the beginning of the page, and under them the content.
On the buttons I put this code:
Scroll to element 1
Scroll to element 2
Scroll to element 3
Scroll to element 4
And under links there will be content:
<h2 id="idElement1">Element1</h2>
content....
<h2 id="idElement2">Element2</h2>
content....
<h2 id="idElement3">Element3</h2>
content....
<h2 id="idElement4">Element4</h2>
content....
It is working now, but cannot make it look more smooth.
I used this code, but cannot get it to work.
$('html, body').animate({
scrollTop: $("#elementID").offset().top
}, 2000);
Any suggestions? Thank you.
Edit: and the fiddle: http://jsfiddle.net/WxJLx/2/

Super smoothly with requestAnimationFrame
For smoothly rendered scrolling animation one could use window.requestAnimationFrame() which performs better with rendering than regular setTimeout() solutions.
A basic example looks like this. Function step is called for browser's every animation frame and allows for better time management of repaints, and thus increasing performance.
function doScrolling(elementY, duration) {
var startingY = window.pageYOffset;
var diff = elementY - startingY;
var start;
// Bootstrap our animation - it will get called right before next frame shall be rendered.
window.requestAnimationFrame(function step(timestamp) {
if (!start) start = timestamp;
// Elapsed milliseconds since start of scrolling.
var time = timestamp - start;
// Get percent of completion in range [0, 1].
var percent = Math.min(time / duration, 1);
window.scrollTo(0, startingY + diff * percent);
// Proceed with animation as long as we wanted it to.
if (time < duration) {
window.requestAnimationFrame(step);
}
})
}
For element's Y position use functions in other answers or the one in my below-mentioned fiddle.
I set up a bit more sophisticated function with easing support and proper scrolling to bottom-most elements:
https://jsfiddle.net/s61x7c4e/

Question was asked 5 years ago and I was dealing with smooth scroll and felt giving a simple solution is worth it to those who are looking for. All the answers are good but here you go a simple one.
function smoothScroll(){
document.querySelector('.your_class or #id here').scrollIntoView({
behavior: 'smooth'
});
}
just call the smoothScroll function on onClick event on your source element.
DOCS: https://developer.mozilla.org/en-US/docs/Web/API/Element/scrollIntoView
Note: Please check compatibility here
3rd Party edit
Support for Element.scrollIntoView() in 2020 is this:
Region full + partial = sum full+partial Support
Asia 73.24% + 22.75% = 95.98%
North America 56.15% + 42.09% = 98.25%
India 71.01% + 20.13% = 91.14%
Europe 68.58% + 27.76% = 96.35%

Just made this javascript only solution below.
Simple usage:
EPPZScrollTo.scrollVerticalToElementById('signup_form', 20);
Engine object (you can fiddle with filter, fps values):
/**
*
* Created by Borbás Geri on 12/17/13
* Copyright (c) 2013 eppz! development, LLC.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
* The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
*/
var EPPZScrollTo =
{
/**
* Helpers.
*/
documentVerticalScrollPosition: function()
{
if (self.pageYOffset) return self.pageYOffset; // Firefox, Chrome, Opera, Safari.
if (document.documentElement && document.documentElement.scrollTop) return document.documentElement.scrollTop; // Internet Explorer 6 (standards mode).
if (document.body.scrollTop) return document.body.scrollTop; // Internet Explorer 6, 7 and 8.
return 0; // None of the above.
},
viewportHeight: function()
{ return (document.compatMode === "CSS1Compat") ? document.documentElement.clientHeight : document.body.clientHeight; },
documentHeight: function()
{ return (document.height !== undefined) ? document.height : document.body.offsetHeight; },
documentMaximumScrollPosition: function()
{ return this.documentHeight() - this.viewportHeight(); },
elementVerticalClientPositionById: function(id)
{
var element = document.getElementById(id);
var rectangle = element.getBoundingClientRect();
return rectangle.top;
},
/**
* Animation tick.
*/
scrollVerticalTickToPosition: function(currentPosition, targetPosition)
{
var filter = 0.2;
var fps = 60;
var difference = parseFloat(targetPosition) - parseFloat(currentPosition);
// Snap, then stop if arrived.
var arrived = (Math.abs(difference) <= 0.5);
if (arrived)
{
// Apply target.
scrollTo(0.0, targetPosition);
return;
}
// Filtered position.
currentPosition = (parseFloat(currentPosition) * (1.0 - filter)) + (parseFloat(targetPosition) * filter);
// Apply target.
scrollTo(0.0, Math.round(currentPosition));
// Schedule next tick.
setTimeout("EPPZScrollTo.scrollVerticalTickToPosition("+currentPosition+", "+targetPosition+")", (1000 / fps));
},
/**
* For public use.
*
* #param id The id of the element to scroll to.
* #param padding Top padding to apply above element.
*/
scrollVerticalToElementById: function(id, padding)
{
var element = document.getElementById(id);
if (element == null)
{
console.warn('Cannot find element with id \''+id+'\'.');
return;
}
var targetPosition = this.documentVerticalScrollPosition() + this.elementVerticalClientPositionById(id) - padding;
var currentPosition = this.documentVerticalScrollPosition();
// Clamp.
var maximumScrollPosition = this.documentMaximumScrollPosition();
if (targetPosition > maximumScrollPosition) targetPosition = maximumScrollPosition;
// Start animation.
this.scrollVerticalTickToPosition(currentPosition, targetPosition);
}
};

Smooth scrolling - look ma no jQuery
Based on an article on itnewb.com i made a demo plunk to smoothly scroll without external libraries.
The javascript is quite simple. First a helper function to improve cross browser support to determine the current position.
function currentYPosition() {
// Firefox, Chrome, Opera, Safari
if (self.pageYOffset) return self.pageYOffset;
// Internet Explorer 6 - standards mode
if (document.documentElement && document.documentElement.scrollTop)
return document.documentElement.scrollTop;
// Internet Explorer 6, 7 and 8
if (document.body.scrollTop) return document.body.scrollTop;
return 0;
}
Then a function to determine the position of the destination element - the one where we would like to scroll to.
function elmYPosition(eID) {
var elm = document.getElementById(eID);
var y = elm.offsetTop;
var node = elm;
while (node.offsetParent && node.offsetParent != document.body) {
node = node.offsetParent;
y += node.offsetTop;
} return y;
}
And the core function to do the scrolling
function smoothScroll(eID) {
var startY = currentYPosition();
var stopY = elmYPosition(eID);
var distance = stopY > startY ? stopY - startY : startY - stopY;
if (distance < 100) {
scrollTo(0, stopY); return;
}
var speed = Math.round(distance / 100);
if (speed >= 20) speed = 20;
var step = Math.round(distance / 25);
var leapY = stopY > startY ? startY + step : startY - step;
var timer = 0;
if (stopY > startY) {
for ( var i=startY; i<stopY; i+=step ) {
setTimeout("window.scrollTo(0, "+leapY+")", timer * speed);
leapY += step; if (leapY > stopY) leapY = stopY; timer++;
} return;
}
for ( var i=startY; i>stopY; i-=step ) {
setTimeout("window.scrollTo(0, "+leapY+")", timer * speed);
leapY -= step; if (leapY < stopY) leapY = stopY; timer++;
}
return false;
}
To call it you just do the following. You create a link which points to another element by using the id as a reference for a destination anchor.
<a href="#anchor-2"
onclick="smoothScroll('anchor-2');">smooth scroll to the headline with id anchor-2<a/>
...
... some content
...
<h2 id="anchor-2">Anchor 2</h2>
Copyright
In the footer of itnewb.com the following is written: The techniques, effects and code demonstrated in ITNewb articles may be used for any purpose without attribution (although we recommend it) (2014-01-12)

You could also check this great Blog - with some very simple ways to achieve this :)
https://css-tricks.com/snippets/jquery/smooth-scrolling/
Like (from the blog)
// Scroll to specific values
// scrollTo is the same
window.scroll({
top: 2500,
left: 0,
behavior: 'smooth'
});
// Scroll certain amounts from current position
window.scrollBy({
top: 100, // could be negative value
left: 0,
behavior: 'smooth'
});
// Scroll to a certain element
document.querySelector('.hello').scrollIntoView({
behavior: 'smooth'
});
and you can also get the element "top" position like below (or some other way)
var e = document.getElementById(element);
var top = 0;
do {
top += e.offsetTop;
} while (e = e.offsetParent);
return top;

Why not use CSS scroll-behavior property
html {
scroll-behavior: smooth;
}
The browser support is also good
https://caniuse.com/#feat=css-scroll-behavior

For a more comprehensive list of methods for smooth scrolling, see my answer here.
To scroll to a certain position in an exact amount of time, window.requestAnimationFrame can be put to use, calculating the appropriate current position each time. To scroll to an element, just set the y-position to element.offsetTop.
/*
#param pos: the y-position to scroll to (in pixels)
#param time: the exact amount of time the scrolling will take (in milliseconds)
*/
function scrollToSmoothly(pos, time) {
var currentPos = window.pageYOffset;
var start = null;
if(time == null) time = 500;
pos = +pos, time = +time;
window.requestAnimationFrame(function step(currentTime) {
start = !start ? currentTime : start;
var progress = currentTime - start;
if (currentPos < pos) {
window.scrollTo(0, ((pos - currentPos) * progress / time) + currentPos);
} else {
window.scrollTo(0, currentPos - ((currentPos - pos) * progress / time));
}
if (progress < time) {
window.requestAnimationFrame(step);
} else {
window.scrollTo(0, pos);
}
});
}
Demo:
function scrollToSmoothly(pos, time) {
var currentPos = window.pageYOffset;
var start = null;
if(time == null) time = 500;
pos = +pos, time = +time;
window.requestAnimationFrame(function step(currentTime) {
start = !start ? currentTime : start;
var progress = currentTime - start;
if (currentPos < pos) {
window.scrollTo(0, ((pos - currentPos) * progress / time) + currentPos);
} else {
window.scrollTo(0, currentPos - ((currentPos - pos) * progress / time));
}
if (progress < time) {
window.requestAnimationFrame(step);
} else {
window.scrollTo(0, pos);
}
});
}
document.getElementById("toElement").addEventListener("click", function(e){
scrollToSmoothly(document.querySelector('div').offsetTop, 500 /* milliseconds */);
});
document.getElementById("backToTop").addEventListener("click", function(e){
scrollToSmoothly(0, 500);
});
<button id="toElement">Scroll To Element</button>
<div style="margin: 1000px 0px; text-align: center;">Div element
<button id="backToTop">Scroll back to top</button>
</div>
The SmoothScroll.js library can also be used, which supports scrolling to an element on the page in addition to more complex features such as smooth scrolling both vertically and horizontally, scrolling inside other container elements, different easing behaviors, scrolling relatively from the current position, and more.
document.getElementById("toElement").addEventListener("click", function(e){
smoothScroll({toElement: document.querySelector('div'), duration: 500});
});
document.getElementById("backToTop").addEventListener("click", function(e){
smoothScroll({yPos: 'start', duration: 500});
});
<script src="https://cdn.jsdelivr.net/gh/LieutenantPeacock/SmoothScroll#1.2.0/src/smoothscroll.min.js" integrity="sha384-UdJHYJK9eDBy7vML0TvJGlCpvrJhCuOPGTc7tHbA+jHEgCgjWpPbmMvmd/2bzdXU" crossorigin="anonymous"></script>
<button id="toElement">Scroll To Element</button>
<div style="margin: 1000px 0px; text-align: center;">Div element
<button id="backToTop">Scroll back to top</button>
</div>
Alternatively, you can pass an options object to window.scroll which scrolls to a specific x and y position and window.scrollBy which scrolls a certain amount from the current position:
// Scroll to specific values
// scrollTo is the same
window.scroll({
top: 2500,
left: 0,
behavior: 'smooth'
});
// Scroll certain amounts from current position
window.scrollBy({
top: 100, // could be negative value
left: 0,
behavior: 'smooth'
});
If you only need to scroll to an element, not a specific position in the document, you can use Element.scrollIntoView with behavior set to smooth.
document.getElementById("elemID").scrollIntoView({
behavior: 'smooth'
});

I've been using this for a long time:
function scrollToItem(item) {
var diff=(item.offsetTop-window.scrollY)/8
if (Math.abs(diff)>1) {
window.scrollTo(0, (window.scrollY+diff))
clearTimeout(window._TO)
window._TO=setTimeout(scrollToItem, 30, item)
} else {
window.scrollTo(0, item.offsetTop)
}
}
usage:
scrollToItem(element) where element is document.getElementById('elementid') for example.

Variation of #tominko answer.
A little smoother animation and resolved problem with infinite invoked setTimeout(), when some elements can't allign to top of viewport.
function scrollToItem(item) {
var diff=(item.offsetTop-window.scrollY)/20;
if(!window._lastDiff){
window._lastDiff = 0;
}
console.log('test')
if (Math.abs(diff)>2) {
window.scrollTo(0, (window.scrollY+diff))
clearTimeout(window._TO)
if(diff !== window._lastDiff){
window._lastDiff = diff;
window._TO=setTimeout(scrollToItem, 15, item);
}
} else {
console.timeEnd('test');
window.scrollTo(0, item.offsetTop)
}
}

you can use this plugin. Does exactly what you want.
http://flesler.blogspot.com/2007/10/jqueryscrollto.html

If one need to scroll to an element inside a div there is my solution based on Andrzej Sala's answer:
function scroolTo(element, duration) {
if (!duration) {
duration = 700;
}
if (!element.offsetParent) {
element.scrollTo();
}
var startingTop = element.offsetParent.scrollTop;
var elementTop = element.offsetTop;
var dist = elementTop - startingTop;
var start;
window.requestAnimationFrame(function step(timestamp) {
if (!start)
start = timestamp;
var time = timestamp - start;
var percent = Math.min(time / duration, 1);
element.offsetParent.scrollTo(0, startingTop + dist * percent);
// Proceed with animation as long as we wanted it to.
if (time < duration) {
window.requestAnimationFrame(step);
}
})
}

Why not use this easy way
Native JS
document.querySelector(".layout").scrollIntoView({
behavior: "smooth",
});

Smooth scrolling with jQuery.ScrollTo
To use the jQuery ScrollTo plugin you have to do the following
Create links where href points to another elements.id
create the elements you want to scroll to
reference jQuery and the scrollTo Plugin
Make sure to add a click event handler for each link that should do smooth scrolling
Creating the links
<h1>Smooth Scrolling with the jQuery Plugin .scrollTo</h1>
<div id="nav-list">
Scroll to element 1
Scroll to element 2
Scroll to element 3
Scroll to element 4
</div>
Creating the target elements here only the first two are displayed the other headings are set up the same way. To see another example i added a link back to the navigation a.toNav
<h2 id="idElement1">Element1</h2>
....
<h2 id="idElement1">Element1</h2>
...
<a class="toNav" href="#nav-list">Scroll to Nav-List</a>
Setting the references to the scripts. Your path to the files may be different.
<script src="./jquery-1.8.3.min.js"></script>
<script src="./jquery.scrollTo-1.4.3.1-min.js"></script>
Wiring it all up
The code below is borrowed from jQuery easing plugin
jQuery(function ($) {
$.easing.elasout = function (x, t, b, c, d) {
var s = 1.70158; var p = 0; var a = c;
if (t == 0) return b;
if ((t /= d) == 1) return b + c;
if (!p) p = d * .3;
if (a < Math.abs(c)) {
a = c; var s = p / 4;
} else var s = p / (2 * Math.PI) * Math.asin(c / a);
// line breaks added to avoid scroll bar
return a * Math.pow(2, -10 * t) * Math.sin((t * d - s)
* (2 * Math.PI) / p) + c + b;
};
// important reset all scrollable panes to (0,0)
$('div.pane').scrollTo(0);
$.scrollTo(0); // Reset the screen to (0,0)
// adding a click handler for each link
// within the div with the id nav-list
$('#nav-list a').click(function () {
$.scrollTo(this.hash, 1500, {
easing: 'elasout'
});
return false;
});
// adding a click handler for the link at the bottom
$('a.toNav').click(function () {
var scrollTargetId = this.hash;
$.scrollTo(scrollTargetId, 1500, {
easing: 'elasout'
});
return false;
});
});
Fully working demo on plnkr.co
You may take a look at the soucre code for the demo.
Update May 2014
Based on another question i came across another solution from kadaj. Here jQuery animate is used to scroll to an element inside a <div style=overflow-y: scroll>
$(document).ready(function () {
$('.navSection').on('click', function (e) {
debugger;
var elemId = ""; //eg: #nav2
switch (e.target.id) {
case "nav1":
elemId = "#s1";
break;
case "nav2":
elemId = "#s2";
break;
case "nav3":
elemId = "#s3";
break;
case "nav4":
elemId = "#s4";
break;
}
$('.content').animate({
scrollTop: $(elemId).parent().scrollTop()
+ $(elemId).offset().top
- $(elemId).parent().offset().top
}, {
duration: 1000,
specialEasing: { width: 'linear'
, height: 'easeOutBounce' },
complete: function (e) {
//console.log("animation completed");
}
});
e.preventDefault();
});
});

html element doesn't move correctly with jQuery

I have to repair bottom slider on http://rhemapress.pl/www_wopr/ . If you see when you click right arrow twice, then animation back to start and animate again. Here when i click one on right arrow time this should be blocked and not possible to click second time.
Numer of moves right is created dynamicly by checkWidth();
function checkWidth() {
var elements = $('.items').children().length;
var width = Math.ceil(elements / 5) * 820;
return width;
}
This return realWidth witch is something like limit of offset. Variable offset is setted to 0 at start. So, if i click right, then in method moveRight() is checked if element can be moved and it's move. At end offset is increment by 820px (one page of slider), so if we've got 2 pages, then next move can't be called. But it is and this is problem! :/
My code
<script type="text/javascript">
$(document).ready(function() {
$('a.prev').bind('click',moveLeft);
$('a.next').bind('click',moveRight);
var realWidth = checkWidth();
realWidth -= 820;
var offset = 0;
function moveLeft(e) {
var position = $('.items').position();
var elements = $('.items').children().length;
if ((elements > 5) && ((offset - 820) >= 0) ) {
$('.items').animate({
'left': (position.left + 820)
}, 300, function() {
offset -= 820;
});
}
}
function moveRight(e) {
var position = $('.items').position();
var elements = $('.items').children().length;
if ((elements > 5) && ((offset + 820) <= realWidth)) {
$('.items').animate({
'left': (position.left - 820)
}, 300, function() {
offset += 820;
});
}
}
function checkWidth() {
var elements = $('.items').children().length;
var width = Math.ceil(elements / 5) * 820;
return width;
}
});
</script>
How can i do this correctly?

It seems like you want to prevent the click event from firing before the current animation is complete. You can do this by preventing the rest of the function from executing if the element is currently being animated:
function moveLeft(e) {
if ($(this).is(":animated")) {
return false;
}

Making an image jump up (and fall back)

I am making a platform game in JavaScript and I need some help.
How do I make an image jump up 50px in JavaScript when the spacebar pushed then fall back to a certain position?

If you mean jumping as in jumping with gravity - you'd need a parabola formula.
E.g.: http://jsfiddle.net/pimvdb/7JFU3/.
var x = 0;
var interval = setInterval(function() {
x++;
image.style.top = 50 - (-0.1 * x * (x - 50)) + 'px';
if(x >= 50) clearInterval(interval);
}, 20);

I'm working on exact the same thing. Here's my github project link https://github.com/beothorn/webcomicsgame
Look at MainCharacter.js at
if(gameCommandState.up){
if(this.canJump(game))
this.element.yAccelerate(-this.yAcceleration);
}
You can fork it if you want, but I'm doing it using canvas.

We had fun extending this to have an image keep bouncing up and down
var x = 0;
var goingUp = true;
var interval = setInterval(function() {
if(goingUp==true) {
x++;
if(x >= 50) {
goingUp=false;
//alert("go down")
}
} else {
x--;
if(x <= -50) {
goingUp=true;
//alert("go up")
}
}
$('#demo').css('top', 50 - (-0.1 * x * (x - 50)));
}, 20);