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jQuery useful preload image effect

Created 12 years ago   Views 13744   downloads 1766    Author wpleet
jQuery useful preload image effect
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The idea is to preload an image first to browser cache, then display it when completely loaded using jQuery. We can also make it more presentable to viewers by adding a fade in effect after we preload image to browser cache.

Create the html holder for the preload image

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>DEMO: How to preload image using jQuery - Javascript</title>
<link rel="stylesheet" type="text/css" href="styles.css" />
</head>
<body>
<div id="content">
    <p>
        <input title="Paste the image url here and click Load Image." id="img_url" type="text"/>
        <button id="load_img">Load Image</button>
    </p>
    <div id="image_content">
        <div id="img_holder" class="loadit"></div>
    </div>
</div>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.5.0/jquery.min.js"></script>
<script src="js/script.js"></script>
</body>
</html>

First step is to lay down the html markup. We also need include jQuery library for use to use some of it’s functionalities.

The Javascript codes:

$(function(){
    LoadImage();
    $("#load_img").click(function(){
        $("#current_img").remove();
        $('#img_holder').addClass('loadit');
        LoadImage();
    });
    function LoadImage(){
        var img_url = $("#img_url").val();
        if(img_url == ''){
            img_url = "images/wetrepubliccomp7c.png";
        }
        var img = new Image();
        $(img).load(function(){
            $(this).hide();
            $('#img_holder').removeClass('loadit').append(img);
            $(img).fadeIn();
        }).attr('src',img_url).attr('id','current_img');
    }
});

To preload an image we will focus on the LoadImage() function. This will server as the main function that drives this tutorial.

var img = new Image();

The idea is to create an Image Object using Javascript, and control the preloading with jQuery using load event.

$(img).load(function(){
    //execute when the event is triggered.
}).attr('src',img_url).attr('id','current_img');

We also need to supply the image attributes first before we preload the image. I added the image source using jQuery function .attr(‘src’,img_url). You can add more attributes on the image like class or id if you like.

$(this).hide();
$('#img_holder').removeClass('loadit').append(img);
$(img).fadeIn();

We will add an event hadler on .load() to control image preloading. I will add a fade in effect to the image before i show it to viewer. Make sure it’s hidden that’s why i called $(this).hide(); , then we will place our img object to $(‘#img_holder’) using .append(img) and use the $(img).fadeIn(); to display it with a fade in effect.

How to call the function

LoadImage();

On a normal page load just call the LoadImage(); function. Be sure to set var img_url with your default image.

$("#load_img").click(function(){
    $("#current_img").remove();
    $('#img_holder').addClass('loadit');
    LoadImage();
});

You can also trigger it on a click event, if you have a project that requires user interaction before you preload an image.

Note:

Load event doesn’t have an error handler built-in, but if you really want to validate first if the image source before you load it, you can use the jQuery ajax request to check it.

$.ajax({
    url: img_url,
    type:'HEAD',
    error:
        function(){
            //Image Not Found!
        },
    success:
        function(){
            //do stuff here if image exist
        }
});

The article source:http://wpleet.com/508-how-to-preload-an-image-using-jquery-javascript/