Develop Reference

How to make a draggable element stay at the new position when dropped (HTML5 not jQuery)?

I have just learned the basics of HTML5 draggable and droppable API. I do not know how to retain the dragged position at its dropped position. On dropping it changes its position.
Here is the basic HTML (relevant elements only):
onDragStart = function(ev) {
//...
}
drop_handler = function(ev) {
ev.preventDefault();
ev.target.appendChild(document.getElementById("id1"));
}
dragover_handler = function(ev) {
ev.preventDefault();
ev.dataTransfer.dropEffect = "move";
}
<div id="id1" draggable="true" ondragstart="onDragStart(event)" style="border:2px solid green; cursor:pointer;width:100px;height:50px;">Dragged Div</div>
<div id="id2" style="position:absolute;left:100px;top:200px;border:2px solid red; cursor:pointer;width:200px;height:200px;" ondrop="drop_handler(event)" ondragover="dragover_handler(event)">Drop Div
</div>
I want the dragged element to remain at its final position where it it is dropped. Any pointers will be appreciated.

As mentioned in my comment, <div id="id1" ...> still has the default positioning which is static. Once you append it to the dropDiv, it assumes normal document flow behavior. Because it's a block element, it goes underneath the text that is already there and fills the width of the block.
If you want it to stay exactly where it is when you drop it, you need to give it position: absolute and take into account how the mouse moved while dragging it on the screen. In the dragStart event, we capture the original coordinates of the dragDiv and account for where the mouse was inside relative to the top-left corner. When we drop the dragDiv into the dropDiv, we set the absolute positioning and account for how much the mouse moved during the drag.
Since dragDiv is now a child of dropDiv, we need our new top and left values to be relative to dropDiv's coordinates rather than the entire screen, so we subtract out dropDiv's top and left values. Note well that some of these methods may not take into account the borders around the elements which may make it look like it's a pixel or two off -- to fix that you can either subtract a one or two pixels in the calculation or give them box-sizing: border-box.
let offsetX;
let offsetY;
onDragStart = function(ev) {
const rect = ev.target.getBoundingClientRect();
offsetX = ev.clientX - rect.x;
offsetY = ev.clientY - rect.y;
};
drop_handler = function(ev) {
ev.preventDefault();
const left = parseInt(id2.style.left);
const top = parseInt(id2.style.top);
id1.style.position = 'absolute';
id1.style.left = ev.clientX - left - offsetX + 'px';
id1.style.top = ev.clientY - top - offsetY + 'px';
id2.appendChild(document.getElementById("id1"));
};
dragover_handler = function(ev) {
ev.preventDefault();
ev.dataTransfer.dropEffect = "move";
};
<div id="id1" draggable="true" ondragstart="onDragStart(event)" style="border:2px solid green; cursor:pointer;width:100px;height:50px;">Dragged Div</div>
<div id="id2" style="position:absolute;left:200px;top:50px;border:2px solid red; cursor:pointer;width:200px;height:200px;" ondrop="drop_handler(event)" ondragover="dragover_handler(event)">Drop Div
</div>

Adjustable page division boundary

I have two columns in my HTML page.
<div id="content">
<div id="left"></div>
<div id="right"></div>
</div>
Each of them occupies half of the page
#content {
height: 100%;
}
#left, #right {
float: left;
width: 50%;
height: 100%;
overflow: auto;
}
I'd like the boundary between left and right halves to be adjustable by the user. That is, the user can move the boundary to the left or to the right as he/she browses the page. Is it possible to do that somehow?

Yes, but it requires JavaScript. To apply it, you could of course just set the width of each of the sides:
var leftPercent = 50;
function updateDivision() {
document.getElementById('left').style.width = leftPercent + '%';
document.getElementById('right').style.width = (100 - leftPercent) + '%';
}
Now you can adjust the division with, say leftPercent = 50; updateDivision(), but the user isn't going to do that. There are multiple different ways you could present this to the user. Probably the best-suited way would be a little line in the middle they could drag. For this, you could use a little CSS for the positioning:
#content {
position: relative;
}
#divider {
position: absolute;
/* left to be set by JavaScript */
width: 1px;
top: 0;
bottom: 0;
background: black;
cursor: col-resize;
/* feel free to customize this, of course */
}
And then make sure you've got a div with an id of divider in content and update updateDivision to also update the left of divider:
document.getElementById('left').style.left = leftPercent + '%';
Then you just need a little logic to handle the dragging. (Here, I've put all of the elements into appropriately-named variables):
divider.addEventListener('mousedown', function(e) {
e.preventDefault();
var lastX = e.pageX;
document.documentElement.addEventListener('mousemove', moveHandler, true);
document.documentElement.addEventListener('mouseup', upHandler, true);
function moveHandler(e) {
e.preventDefault();
e.stopPropagation();
var deltaX = e.pageX - lastX;
lastX = e.pageX;
leftPercent += deltaX / parseFloat(document.defaultView.getComputedStyle(content).width) * 100;
updateDivision();
}
function upHandler(e) {
e.preventDefault();
e.stopPropagation();
document.documentElement.removeEventListener('mousemove', moveHandler, true);
document.documentElement.removeEventListener('mouseup', upHandler, true);
}
}, false);
You should be able to read it to see how it works, but in short: It listens for when someone presses on the divider. When they do, it'll attach listeners to the page for when they move their mouse. When they do, it updates the variable and calls updateDivision to update the styles. When eventually it gets a mouseup, it stops listening on the page.
As a further improvement, you could make every element have an appropriate cursor style while dragging so your cursor doesn't flash while dragging it.
Try it out.

There's nothing in the divisions so nothing will happen. It's like writing:
<h1></h1>
And changing the CSS for h1 and expecting something to be there

Scroll event background change

I am trying to add a scroll event which will change the background of a div which also acts as the window background (it has 100% width and height). This is as far as I get. I am not so good at jquery. I have seen tutorials with click event listeners. but applying the same concept , like, returning scroll event as false, gets me nowhere. also I saw a tutorial on SO where the person suggest use of array. but I get pretty confused using arrays (mostly due to syntax).
I know about plugins like waypoints.js and skrollr.js which can be used but I need to change around 50-60 (for the illusion of a video being played when scrolled) ... but it wont be feasible.
here is the code im using:-
*
{
border: 2px solid black;
}
#frame
{
background: url('1.jpg') no-repeat;
height: 1000px;
width: 100%;
}
</style>
<script>
$(function(){
for ( i=0; i = $.scrolltop; i++)
{
$("#frame").attr('src', ''+i+'.jpg');
}
});
</script>
<body>
<div id="frame"></div>
</body>

Inside your for loop, you are setting the src attribute of #frame but it is a div not an img.
So, instead of this:
$("#frame").attr('src', ''+i+'.jpg');
Try this:
$("#frame").css('background-image', 'url(' + i + '.jpg)');
To bind a scroll event to a target element with jQuery:
$('#target').scroll(function() {
//do stuff here
});
To bind a scroll event to the window with jQuery:
$(window).scroll(function () {
//do stuff here
});
Here is the documentation for jQuery .scroll().
UPDATE:
If I understand right, here is a working demo on jsFiddle of what you want to achieve.
CSS:
html, body {
min-height: 1200px; /* for testing the scroll bar */
}
div#frame {
display: block;
position: fixed; /* Set this to fixed to lock that element on the position */
width: 300px;
height: 300px;
z-index: -1; /* Keep the bg frame at the bottom of other elements. */
}
Javascript:
$(document).ready(function() {
switchImage();
});
$(window).scroll(function () {
switchImage();
});
//using images from dummyimages.com for demonstration (300px by 300px)
var images = ["http://dummyimage.com/300x300/000000/fff",
"http://dummyimage.com/300x300/ffcc00/000",
"http://dummyimage.com/300x300/ff0000/000",
"http://dummyimage.com/300x300/ff00cc/000",
"http://dummyimage.com/300x300/ccff00/000"
];
//Gets a valid index from the image array using the scroll-y value as a factor.
function switchImage()
{
var sTop = $(window).scrollTop();
var index = sTop > 0 ? $(document).height() / sTop : 0;
index = Math.round(index) % images.length;
//console.log(index);
$("#frame").css('background-image', 'url(' + images[index] + ')');
}
HTML:
<div id="frame"></div>
Further Suggestions:
I suggest you change the background-image of the body, instead of the div. But, if you have to use a div for this; then you better add a resize event-istener to the window and set/update the height of that div with every resize. The reason is; height:100% does not work as expected in any browser.

I've done this before myself and if I were you I wouldn't use the image as a background, instead use a normal "img" tag prepend it to the top of your page use some css to ensure it stays in the back under all of the other elements. This way you could manipulate the size of the image to fit screen width better. I ran into a lot of issues trying to get the background to size correctly.
Html markup:
<body>
<img src="1.jpg" id="img" />
</body>
Script code:
$(function(){
var topPage = 0, count = 0;
$(window).scroll( function() {
topPage = $(document).scrollTop();
if(topPage > 200) {
// function goes here
$('img').attr('src', ++count +'.jpg');
}
});
});
I'm not totally sure if this is what you're trying to do but basically, when the window is scrolled, you assign the value of the distance to the top of the page, then you can run an if statement to see if you are a certain point. After that just simply change run the function you would like to run.
If you want to supply a range you want the image to change from do something like this, so what will happen is this will allow you to run a function only between the specificied range between 200 and 400 which is the distance from the top of the page.
$(function(){
var topPage = 0, count = 0;
$(window).scroll( function() {
topPage = $(document).scrollTop();
if(topPage > 200 && topPage < 400) {
// function goes here
$('#img').attr('src', ++count +'.jpg');
}
});
});

Using jQuery .on() when selector element is obscured by another element

I'm trying to get my jQuery event callback to trigger correctly, but I can't seem to get around the fact the element I am interested in not receiving the event because of another element that covers it on the page. I can summarise it as follows (I've styled the elements so they show up in a jsfiddle):
<div id='mydiv'>
<div style="border: 1px solid; border-color: red; position: absolute; left: 0px; top: 0px; width: 200px; height: 200px; z-index: 100">Hello</div>
<canvas style="border: 1px solid; border-color: yellow; position: absolute; left: 50px; top: 50px; width: 150px; height: 150px"></canvas>
</div>​
With the segment above, if I try to listen to mouse clicks on the <canvas>, the event never gets called:
$('#mydiv').on('mousedown', 'canvas', this, function(ev) {
console.log(ev.target);
});
However, if I modify my event handler to listen to the <div> element instead, the callback is triggered as expected:
$('#mydiv').on('mousedown', 'div', this, function(ev) {
console.log(ev.target);
});
How can I coerce my <canvas> to receive events, whilst leaving the offending <div> block in the fore-front?

This should be the simplest solution, as already proposed:
http://jsfiddle.net/CUJ68/4/
$('canvas').on('mousedown', function(ev) {
console.log(ev.target);
});
$('ul').on('mousedown', function(ev){
$('canvas').mousedown();
});
if you need the original eventdata:
$('canvas').bind('mousedown', function(ev, parentEV) {
if(parentEV){
console.log(parentEV);
alert("Canvas INdirectly clicked!");
}else{
console.log(ev);
alert("Canvas directly clicked!");
}
});
$('ul').on('mousedown', function(ev){
$('canvas').trigger('mousedown', ev);
});

You can't. Objects on top get the click events. That's how the DOM works.
If you want to handle that click event, you will need to handle in the object that is on top or use bubbling and handle it in a parent object. You can handle it in the top object and "forward" it to the other object if you want by triggering a click on that other object or by just calling a click handler directly.
Or, you can move the canvas element above the ul by setting it's z-index to a higher value and it will then get the click event.
Or, you can make a new transparent canvas object that is on top that gets the event, leaving the other two objects where they are for the desired visual effect.

You can bind the element to the closest common parent, and check whether the X and Y coordinates of the mouse are within the range of the canvas.
In the example below, I have cached the dimensions (height and width) of the canvas, because I assume these to be constant. Move this inside the function if the dimensions are not constant.
I use the .offset() method to calculate the real X and Y coordinates of the <canvas>s top-left corner. I calculate the coordinates of the bottom-right corner by adding the values of outerWidth() and .outerHeight().
Basic demo: http://jsfiddle.net/75qbX/2/
var $canvas = $('canvas'), /* jQuery reference to the <canvas> */
$canvasWidth = $canvas.outerWidth(), /* assuming height and width to be constant */
$canvasHeight = $canvas.outerHeight();
function isCanvasClicked(x, y, target) {
if (target.tagName === 'CANVAS') return true;
var offset = $canvas.offset(),
left = offset.left,
top = offset.top;
return x >= left && x <= left + $canvasWidth &&
y >= top && y <= top + $canvasHeight;
}
$('#mydiv').on('mousedown', '*', this, function(ev) {
if (isCanvasClicked(ev.pageX, ev.pageY, ev.target)) {
$canvas.fadeOut().fadeIn();
}
});

Here you have a solution that consists in capture click event on above element, and triggering the event on the other: registering clicks on an element that is under another element

jQuery/JavaScript collision detection

How to detect if two <div> elements have collided?
The two divs are simple coloured boxes travelling perpendicular to each other, so no complicated shapes or angles.

var overlaps = (function () {
function getPositions( elem ) {
var pos, width, height;
pos = $( elem ).position();
width = $( elem ).width();
height = $( elem ).height();
return [ [ pos.left, pos.left + width ], [ pos.top, pos.top + height ] ];
}
function comparePositions( p1, p2 ) {
var r1, r2;
r1 = p1[0] < p2[0] ? p1 : p2;
r2 = p1[0] < p2[0] ? p2 : p1;
return r1[1] > r2[0] || r1[0] === r2[0];
}
return function ( a, b ) {
var pos1 = getPositions( a ),
pos2 = getPositions( b );
return comparePositions( pos1[0], pos2[0] ) && comparePositions( pos1[1], pos2[1] );
};
})();
$(function () {
var area = $( '#area' )[0],
box = $( '#box0' )[0],
html;
html = $( area ).children().not( box ).map( function ( i ) {
return '<p>Red box + Box ' + ( i + 1 ) + ' = ' + overlaps( box, this ) + '</p>';
}).get().join( '' );
$( 'body' ).append( html );
});
body {
padding: 30px;
color: #444;
font-family: Arial, sans-serif;
}
h1 {
font-size: 24px;
margin-bottom: 20px;
}
#area {
border: 2px solid gray;
width: 500px;
height: 400px;
position: relative;
}
#area > div {
background-color: rgba(122, 122, 122, 0.3);
position: absolute;
text-align: center;
font-size: 50px;
width: 60px;
height: 60px;
}
#box0 {
background-color: rgba(255, 0, 0, 0.5) !important;
top: 150px;
left: 150px;
}
#box1 {
top: 260px;
left: 50px;
}
#box2 {
top: 110px;
left: 160px;
}
#box3 {
top: 200px;
left: 200px;
}
#box4 {
top: 50px;
left: 400px;
}
p {
margin: 5px 0;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.1/jquery.min.js"></script>
<h1>Detect overlapping with JavaScript</h1>
<div id="area">
<div id="box0"></div>
<div id="box1">1</div>
<div id="box2">2</div>
<div id="box3">3</div>
<div id="box4">4</div>
</div>
General idea - you get the offset and dimension of the boxes and check whether they overlap.
If you want it to update, you can use setInterval:
function detectOverlapping() {
// code that detects if the box overlaps with a moving box
setInterval(detectOverlapping, 25);
}
detectOverlapping();
Also, note that you can optimize the function for your specific example.
you don't have to read the box dimensions repeatedly (like I do in my code) since they are fixed. You can read them on page load (into a variable) and then just read the variable
the horizontal position of the little box does not change (unless the user resizes the window). The vertical positions of the car boxes does not change. Therefore, those values also do not have to be read repeatedly, but can also be stored into variables.
you don't have to test whether the little box overlaps with all car boxes at all times. You can - based on its vertical position - figure out in which lane the box is currently, and test only the specific car box from that lane.

I believe this is the easiest way:
https://plugins.jquery.com/overlaps/
Here is another one, in German:
http://www.48design.de/news/2009/11/20/kollisionsabfrage-per-jquery-plugin-update-v11-8/
I'd give those a try.
--UPDATE--
I can't really spend anytime on it right now, but i can when i get home if no one answers but you;d do something like:
setInterval(function(){
//First step would be to get the offset of item 1 and item 2
//Second would be to get the width of each
//Third would be to check if the offset+width ever overlaps
//the offset+width of the 2nd
//Fourth would be, if so, do X or set a class...
},10);

Its a little late on this but I guess you could use this approach that I tried when I was faced with the similar situation. The advantage here is that there are no additional plugin, or scripts involved and neither do you have to introduce performance hungry polling into it.
This technique uses the the built-in methods and events that Jquery's droppable has to offer.
Ok, enough said, here's the solution technique:
Say if you have two elements (images in my case) and you don't want them to overlap or detect when they do, make the two elements a droppable and make them to 'accept' each other:
$([div1, div2]).droppable(CONFIG_COLLISSION_PREVENTION_DROPPABLE);
The 'CONFIG_COLLISSION_PREVENTION_DROPPABLE' looks like this:
var originatingOffset = null;
CONFIG_COLLISSION_PREVENTION_DROPPABLE = {
tolerance: "touch",
activate : function (event, ui) {
// note the initial position/offset when drag starts
// will be usedful in drop handler to check if the move
// occurred and in cae overlap occurred, restore the original positions.
originatingOffset = ui.offset;
},
drop : function (event, ui) {
// If this callback gets invoked, the overlap has occurred.
// Use this method to either generate a custom event etc.
// Here, i used it to nullify the move and resetting the dragged element's
// position back to it's original position/offset
// (which was captured in the 'activate' handler)
$(ui.draggable).animate({
top: originatingOffset.top + "px",
left: originatingOffset.left + "px"
}, 300);
}
}
The 'activate' and 'drop' handlers refer to the 'dropactivate' and 'drop' events of "droppable" plugin
Here, the key is the 'drop' callback. Whenever any of the two elements overlap and they are dropped over each other, the 'drop' will be called. This is the place to detect and take actions, may be sending out custom events or calling other actions (I here chose to revert the overlapping element's positions to the initial position when the drag started, which was captured in 'activate' callback).
That's it. No polling, no plugins, just the built-in events.
Well, there can be other optimizations/extensions done to it, this was simply the first shot out of my head that worked :)
You can also use the 'dropover' and 'dropout' events to signal and create a visual feedback to the user that two elements are overlapping, while they may be still on the move.
var CLASS_INVALID = "invalid";
// .invalid { border: 1px solid red; }
...
$.extend(CONFIG_COLLISSION_PREVENTION_DROPPABLE, {
over : function (event, ui) {
// When an element is over another, it gets detected here;
// while it may still be moved.
// the draggable element becomes 'invalid' and so apply the class here
$(ui.draggable).addClass(CLASS_INVALID);
},
out : function(event, ui) {
// the element has exited the overlapped droppable now
// So element is valid now and so remove the invalid class from it
$(ui.draggable).removeClass(CLASS_INVALID);
}
});
Hope this helps!

You can do this using getBoundingClientRect()
function isOverlapping(div1, div2){
const div1 = div1.getBoundingClientRect();
const div2 = div2.getBoundingClientRect();
return (div1.right > div2.left &&
div1.left < div2.right &&
div1.bottom > div2.top &&
div1.top < div2.bottom)
}

EDIT: I have written a blog post on my website. Here a link to it.
http://area36.nl/2014/12/creating-your-own-collision-detection-function-in-javascript/
Well I had the same problem but thanks to the answer of Oscar Godson I got a function that works. I used Jquery for easy coding and because i'm lazy ;p. I put the function in a other function that is fired every second so keep that in mind.
function collidesWith (element1, element2) {
var Element1 = {};
var Element2 = {};
Element1.top = $(element1).offset().top;
Element1.left = $(element1).offset().left;
Element1.right = Number($(element1).offset().left) + Number($(element1).width());
Element1.bottom = Number($(element1).offset().top) + Number($(element1).height());
Element2.top = $(element2).offset().top;
Element2.left = $(element2).offset().left;
Element2.right = Number($(element2).offset().left) + Number($(element2).width());
Element2.bottom = Number($(element2).offset().top) + Number($(element2).height());
if (Element1.right > Element2.left && Element1.left < Element2.right && Element1.top < Element2.bottom && Element1.bottom > Element2.top) {
// Do your stuff here
}
}
What it does is basically it gets all the values of element1 and then get all the values of element2. Then with the help of some calculations it figures out all the values. Then in the if statement it compares the square of element1 to the square of element2. If the values of element1 are between the left, right, top and bottom values of element2. If that is true the code in the bottom is executed.

I ran into this generalized issue myself, so (full disclosure) I made a plugin for it. For simple collision queries about static objects, try this:
http://sourceforge.net/projects/jquerycollision/
Which allows you to get a list of overlapping collision boxes (or none if there's no collision):
hits = $("#collider").collision(".obstacles");
Or to get a collision event during "dragging", use this:
http://sourceforge.net/apps/mediawiki/jquidragcollide/?source=navbar#collision
Which gives you a "collision" event to connect to. (Or a "protrusion" event, to see if a div escapes another div that currently contains it.)
$(draggable).bind(
"collision",
function(event,ui) {
...
}
);
If you are checking collisions during motion other than dragging, just call the original repeatedly, it's pretty quick. Note: the dragging one doesn't play nicely with resizing.

Post is old, May be it help someone...
function CheckDiv()
{
var ediv1 = document.getElementById('DIV1');
var ediv2 = document.getElementById('DIV2');
ediv1.top = $(ediv1).offset().top;
ediv1.left = $(ediv1).offset().left;
ediv1.right = Number($(ediv1).offset().left) + Number($(ediv1).width());
ediv1.bottom = Number($(ediv1).offset().top) + Number($(ediv1).height());
ediv2.top = $(ediv2).offset().top;
ediv2.left = $(ediv2).offset().left;
ediv2.right = Number($(ediv2).offset().left) + Number($(ediv2).width());
ediv2.bottom = Number($(ediv2).offset().top) + Number($(ediv2).height());
if (ediv1.right > ediv2.left && ediv1.left < ediv2.right && ediv1.top < ediv2.bottom && ediv1.bottom > ediv2.top)
{
alert("hi");
}
if (ediv1.left > ediv2.left && ediv1.top > ediv2.top && ediv1.right < ediv2.right && ediv1.bottom < ediv2.bottom)
{
alert("hello");
}
}