CODEWITHSUNDEEP
javascripthtmlimageweb-worker
Developer Desk
Developer Desk

Reputation: 2344

How to load images using web worker?

I am trying to load images using webworker api. I have large images in my html page its takes 5 mins to load all images therefore i am using webworker to load images.

here is technique..

  1. I am keeping src attribute of all img tag empty in html page.

  2. All images have unique id for each img e.g id = events_all_1_01 meaning image src will be "pictures/keywords/events/all/1/01.jpg". i.e last part events/all/1/01.jpg is id.

Main.html file 

 <body>  
    <script src="js/modernizr.custom.js"></script>
    <script language="javascript">
       window.onload = function(){   
        if (Modernizr.webworkers) {               
            var worker = new Worker('js/webworker/test_ww_23_04.js');  
            worker.onmessage = function(event) {
                var url = event.data.replace(/_/g, "/");
                var image_src = "pictures/keywords/"+url+".jpg";
                var img = new Image();
                img.src = image_src;     
                img.onload = function(){
                    // do stuff when your image is loaded
                    document.getElementById(event.data).src = image_src;
                }                          
            };

            worker.onerror = function(e) {
                alert('Error: Line ' + e.lineno + ' in ' + e.filename + ': ' + e.message);
            };

                var img_container = document.getElementById("wrapper");
                var image_array = img_container.getElementsByTagName('img');
                for(var i=0;i<image_array.length;i++){
                    var img_id = image_array[i].id;
                    console.log(img_id);  // http://jsfiddle.net/5vyseob7/
                    postMessage(img_id); // http://jsfiddle.net/k04t6760/ here i am passing id one by one to webworker..
                }
            } // end of if condition                                             
        } // end of window.onload()

    </script>  
    <div id="wrapper" style="height: 500px;width: 200px;overflow-y: auto;border: 1px solid gray;">
        <div id="pictures1">
            <div class="effect-1">
                <div><img src="" id="events_all_1_01" width="150" height="100"></div>
                <div><img src="" id="events_all_1_02" width="150" height="100"></div>
                <div><img src="" id="events_all_1_03" width="150" height="100"></div>
                <div><img src="" id="events_all_1_04" width="150" height="100"></div>
            </div>
            <hr/>
            <div class="effect-2">
                <div><img src="" id="events_all_2_01" width="150" height="100"></div>
                <div><img src="" id="events_all_2_02" width="150" height="100"></div>
                <div><img src="" id="events_all_2_03" width="150" height="100"></div>
                <div><img src="" id="events_all_2_04" width="150" height="100"></div>
            </div>
            <hr/>
            <div class="effect-3">
                <div><img src="" id="events_all_3_01" width="150" height="100"></div>
                <div><img src="" id="events_all_3_02" width="150" height="100"></div>
                <div><img src="" id="events_all_3_03" width="150" height="100"></div>
                <div><img src="" id="events_all_3_04" width="150" height="100"></div>
            </div>
            <hr/>
            <div class="effect-4">
                <div><img src="" id="events_all_4_01" width="150" height="100"></div>
                <div><img src="" id="events_all_4_02" width="150" height="100"></div>
                <div><img src="" id="events_all_4_03" width="150" height="100"></div>
                <div><img src="" id="events_all_4_04" width="150" height="100"></div>
            </div>
        </div>
    </div>
</body>

webworker code.

 //var src = 'pictures/keywords/events/all/1/01.jpg';
 //var id = src.substring(src.substring(0,18).length).split('.')[0].replace(/\//g, "_"); // Creating id here......events_all_1_01
 //var fst = id.substring(0, id.lastIndexOf("_")+1); // get first part.... events_all_1
 //var lst = parseInt(id.substr(id.lastIndexOf("_")+1)); // get last part i.e imagename ..01,02,03 etc....... and convert it to int

    function LoadImages(currID) {
            setTimeout(function() {
                postMessage(currID); 
            }, 100);  
    }
    self.onmessage = function(event) {
        var currID = event.data;
        LoadImages(currID); 
    };

I am getting following error :

Uncaught SyntaxError: Failed to execute 'postMessage' on 'Window': Invalid target origin '' in a call to 'postMessage'.

Upvotes: 10

Views: 9340

Answers (1)

rafaelcastrocouto
rafaelcastrocouto

Reputation: 12161

Typo error:

...
worker.onmessage = function(event) {
  var url = e.data.replace(/_/g, "/");

e is not defined ... you probably meant function(e) or event.data.replace

UPDATE

Window don't have the postMessage method ... you need to use the worker method worker.postMessage

Upvotes: 3

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