jQuery: How can I create a simple overlay?

How can I create a really basic overlay in jQuery without UI?

What is a lightweight plugin?

An overlay is, simply put, a div that stays fixed on the screen (no matter if you scroll) and has some sort of opacity.

This will be your CSS for cross browser opacity of 0.5:

#overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: #000;
    filter:alpha(opacity=50);
    -moz-opacity:0.5;
    -khtml-opacity: 0.5;
    opacity: 0.5;
    z-index: 10000;
}

This will be your jQuery code (no UI needed). You're just going to create a new element with the ID #overlay. Creating and destroying the DIV should be all you need.

var overlay = jQuery('<div id="overlay"> </div>');
overlay.appendTo(document.body)

For performance reasons you might wanna have the DIV hidden and setting the display to block and none as you need it or not.

Hope it helps!

Edit: As @Vitaly so well put it, be sure to check your DocType. Read more on the comments on his findings..

Here is a simple javascript only solution

function displayOverlay(text) {
	$("<table id='overlay'><tbody><tr><td>" + text + "</td></tr></tbody></table>").css({
		"position": "fixed",
		"top": 0,
		"left": 0,
		"width": "100%",
		"height": "100%",
		"background-color": "rgba(0,0,0,.5)",
		"z-index": 10000,
		"vertical-align": "middle",
		"text-align": "center",
		"color": "#fff",
		"font-size": "30px",
		"font-weight": "bold",
		"cursor": "wait"
	}).appendTo("body");
}

function removeOverlay() {
	$("#overlay").remove();
}

Demo:

http://jsfiddle.net/UziTech/9g0pko97/

Gist:

https://gist.github.com/UziTech/7edcaef02afa9734e8f2

Here's a fully encapsulated version which adds an overlay (including a share button) to any IMG element where data-photo-overlay='true.

JSFiddle http://jsfiddle.net/wloescher/7y6UX/19/

HTML

<img id="my-photo-id" src="http://cdn.sstatic.net/stackexchange/img/logos/so/so-logo.png" alt="Photo" data-photo-overlay="true" />

CSS

#photoOverlay {
    background: #ccc;
    background: rgba(0, 0, 0, .5);
    display: none;
    height: 50px;
    left: 0;
    position: absolute;
    text-align: center;
    top: 0;
    width: 50px;
    z-index: 1000;
}

#photoOverlayShare {
    background: #fff;
    border: solid 3px #ccc;
    color: #ff6a00;
    cursor: pointer;
    display: inline-block;
    font-size: 14px;
    margin-left: auto;
    margin: 15px;
    padding: 5px;
    position: absolute;
    left: calc(100% - 100px);
    text-transform: uppercase;
    width: 50px;
}

JavaScript

(function () {
    // Add photo overlay hover behavior to selected images
    $("img[data-photo-overlay='true']").mouseenter(showPhotoOverlay);
    
    // Create photo overlay elements
    var _isPhotoOverlayDisplayed = false;
    var _photoId;
    var _photoOverlay = $("<div id='photoOverlay'></div>");
    var _photoOverlayShareButton = $("<div id='photoOverlayShare'>Share</div>");
    
    // Add photo overlay events
    _photoOverlay.mouseleave(hidePhotoOverlay);
    _photoOverlayShareButton.click(sharePhoto);
    
    // Add photo overlay elements to document
    _photoOverlay.append(_photoOverlayShareButton);
    _photoOverlay.appendTo(document.body);
    
    // Show photo overlay
    function showPhotoOverlay(e) {
        // Get sender 
        var sender = $(e.target || e.srcElement);
        
        // Check to see if overlay is already displayed
        if (!_isPhotoOverlayDisplayed) {
            // Set overlay properties based on sender
            _photoOverlay.width(sender.width());
            _photoOverlay.height(sender.height());
            
            // Position overlay on top of photo
            if (sender[0].x) {
                _photoOverlay.css("left", sender[0].x + "px");
                _photoOverlay.css("top", sender[0].y) + "px";
            }
            else {
                // Handle IE incompatibility
                _photoOverlay.css("left", sender.offset().left);
                _photoOverlay.css("top", sender.offset().top);
            }
            
            // Get photo Id
            _photoId = sender.attr("id");
            
            // Show overlay
            _photoOverlay.animate({ opacity: "toggle" });
            _isPhotoOverlayDisplayed = true;
        }
    }
    
    // Hide photo overlay
    function hidePhotoOverlay(e) {
        if (_isPhotoOverlayDisplayed) {
            _photoOverlay.animate({ opacity: "toggle" });
            _isPhotoOverlayDisplayed = false;
        }
    }
    
    // Share photo
    function sharePhoto() {
        alert("TODO: Share photo. [PhotoId = " + _photoId + "]");
        }
    }
)();

If you're already using jquery, I don't see why you wouldn't also be able to use a lightweight overlay plugin. Other people have already written some nice ones in jquery, so why re-invent the wheel?

Please check this jQuery plugin,

blockUI

with this you can overlay all the page or elements, works great for me,

Examples: Block a div:

$('div.test').block({ message: null }); 

Block the page:

$.blockUI({ message: '<h1><img src="busy.gif" /> Just a moment...</h1>' });

Hope that help someone

Greetings

By overlay do you mean content that overlaps/covers the rest of the page? In HTML, you could do this by using a div that uses absolute or fixed positioning. If it needed to be generated dynamically, jQuery could simply generate a div with the position style set appropriately.

What do you intend to do with the overlay? If it's static, say, a simple box overlapping some content, just use absolute positioning with CSS. If it's dynamic (I believe this is called a lightbox), you can write some CSS-modifying jQuery code to show/hide the overlay on-demand.