Using HTML5 Web Worker: Introducing Multithreading in JavaScript

Problem with JavaScript is that it is single thread environment. Every thing we do in JavaScript is managed and calculated by single thread.

Sometimes it happen that you have some more computation intensive task and your webpage performance may degrade(e.g. UI animation or transition performance). In this case, To achieve Parallelism, you can use Worker interface to spawn a new thread in background to do complicated calculation.

Worker thread can not directly communicate with Main thread, that means you can not directly change the content of any element in webpage(i.e. Inside Worker thread you can not run document.getElementById("demo").innerHTML = "demo";. You can not even alert from worker).

When to use Web Worker?

In case if your webpage have some code that is always running in the background like sorting algorithms, finding new position for animation, sine-cosine calculation etc.

Creating new Web Worker

You can create a new Web Worker using Worker() Constructor with Script location as argument.

var worker = new Worker("test_worker.js");

Setting Listener on Worker Thread

You can set Listener on Worker to receive message from Worker thread as following:

worker.addEventListener('message', function(e) { //Your action code goes here //received dataa will be in e.data alert(e.data); }, false);

Third argument here is useCapture. You can Google it for more help. You can also set Listener as following:

worker.onmessage = function (e) { //Your action code goes here alert(e.data); }

You can use either of this way to set Listener on Worker

In "test_worker.js", you can set Listener to receiver message from Main Thread as following:

self.addEventListener('message', function(e) { //Your action code goes here i = i + 1; self.postMessage(i); }, false);

Same way you can also use following method:

var i = 0; self.onmessage = function (e) { //Your action code goes here i = i + 1; self.postMessage(i); }

Here, postMessage() method is used to send message from Worker thread to Main thread and vice versa.

You can terminate Worker Thread using terminate() method:

worker.terminate();

Combining all this together, you can write your Multithreaded code for your highly computation intensive task, Which in turn will improve performance of web application.

Liked What You Read? Take a Next Step. Share It (Click Below) !! Let Others Know.

---

Related Post(s):

• How to use Python in Web Application Development ?
• How create Web application with OpenShift using Eclipse
• How to Include Your Website in Google Search Result
• How to Create Free Webpage Hit Counter?
• How to Install MongoDB (NoSQL database) on Windows 7?

How to Add Numbered Page Navigation Widget for Blogger

In Blogger, we have the option to set the number of posts we want to display per page by going to the Settings menu > Posts and comments > Show at most ? posts. Once the number of total posts in our blog exceeds this number, we will see "Older Posts" and "Newer Posts" navigation links in our home page and archive pages footer as Blogger doesn't have any built-in function on page numbering. But page numbers instead of older and newer posts links could help our blog visitors to navigate quicker (jump from one page to another page or click on a specific page) and know the total number of posts published. Here's a tutorial on how to add numbered page navigation using Javascript to a Blogger/ blogspot blog. You can select any one of the 7 different styles that I have mentioned below.

Adding Numbered Page Navigation to Blogger

You can add this widget in just two steps.
1. Adding The CSS.
2. Adding The Script.

Now let's see how to add the CSS style for page navigation.

1. Adding The CSS

Step 1. Go to Blogger Dashboard > Template > click on the Edit HTML button:

Step 2. Click anywhere inside the code area and press the CTRL + F keys to open the Blogger search box.

... type or paste the following tag inside the search box and hit Enter to find it:

]]></b:skin>

Step 3. Now choose one of the following numbered page navigation styles and copy the code just below it. Just above ]]></b:skin> paste the code of the style that you want to use:

Style 1

 #blog-pager{clear:both;margin:30px auto;text-align:center; padding: 7px;}
.blog-pager {background: none;}
.displaypageNum a,.showpage a,.pagecurrent{padding: 3px 7px;margin-right:5px;background:#E9E9E9;color: #888;border:1px solid #E9E9E9;}
.displaypageNum a:hover,.showpage a:hover,.pagecurrent{background:#CECECE;text-decoration:none;color: #000;}
 .showpageOf{display:none!important}
#blog-pager .showpage, #blog-pager .pagecurrent{font-weight:bold;color: #888;}
 #blog-pager .pages{border:none;}

Style 2:

 #blog-pager{clear:both;margin:30px auto;text-align:center; padding: 7px;}
.blog-pager {background: none;}
.displaypageNum a,.showpage a,.pagecurrent{padding: 5px 10px;margin-right:5px; color: #F4F4F4; background-color:#404042;-webkit-box-shadow: 0px 5px 3px -1px rgba(50, 50, 50, 0.53);-moz-box-shadow:0px 5px 3px -1px rgba(50, 50, 50, 0.53);box-shadow: 0px 5px 3px -1px rgba(50, 50, 50, 0.53);}
.displaypageNum a:hover,.showpage a:hover, .pagecurrent{background:#EC8D04;text-decoration:none;color: #fff;}
#blog-pager .showpage, #blog-pager, .pagecurrent{font-weight:bold;color: #000;}
 .showpageOf{display:none!important}
#blog-pager .pages{border:none;-webkit-box-shadow: 0px 5px 3px -1px rgba(50, 50, 50, 0.53);-moz-box-shadow:0px 5px 3px -1px rgba(50, 50, 50, 0.53);box-shadow: 0px 5px 3px -1px rgba(50, 50, 50, 0.53);}

Style 3:

 #blog-pager{clear:both;margin:30px auto; padding: 7px; text-align:center;font-size: 11px;background-image: -webkit-gradient(linear,left bottom,left top,color-stop(0, #000000),color-stop(1, #292929));background-image: -o-linear-gradient(top, #000000 0%, #292929 100%);background-image: -moz-linear-gradient(top, #000000 0%, #292929 100%);background-image: -webkit-linear-gradient(top, #000000 0%, #292929 100%);background-image: -ms-linear-gradient(top, #000000 0%, #292929 100%);background-image: linear-gradient(to top, #000000 0%, #292929 100%); padding: 6px;-webkit-border-radius: 3px;-moz-border-radius: 3px;border-radius: 3px;}
.blog-pager {background: none;}
.displaypageNum a,.showpage a,.pagecurrent{padding: 3px 10px;margin-right:5px; color: #fff;}
.displaypageNum a:hover,.showpage a:hover,.pagecurrent{background-image: -webkit-gradient(linear,left bottom,left top,color-stop(0, #59A2CF),color-stop(1, #D9EAFF));background-image: -o-linear-gradient(top, #59A2CF 0%, #D9EAFF 100%);background-image: -moz-linear-gradient(top, #59A2CF 0%, #D9EAFF 100%);background-image: -webkit-linear-gradient(top, #59A2CF 0%, #D9EAFF 100%);background-image: -ms-linear-gradient(top, #59A2CF 0%, #D9EAFF 100%);background-image: linear-gradient(to top, #59A2CF 0%, #D9EAFF 100%);text-decoration: none;color: #000;-webkit-border-radius: 3px;-moz-border-radius: 3px;border-radius: 3px;}
.showpageOf{display:none!important}.blog-pager-older-link, .home-link, .blog-pager-newer-link {background: transparent;}
a.blog-pager-older-link, a.home-link, a.blog-pager-newer-link {color: #fff;}
#blog-pager .pages{border:none;background: none;}

Style 4:

#blog-pager{clear:both;margin:30px auto;text-align:center; padding: 7px;}
.blog-pager {background: none;}
.displaypageNum a,.showpage a,.pagecurrent{font-size: 14px;padding: 5px 12px;margin-right:5px; color: #666; background-color:#eee;}
.displaypageNum a:hover,.showpage a:hover, .pagecurrent{background:#359BED;text-decoration:none;color: #fff;}
#blog-pager .pagecurrent{font-weight:bold;color: #fff;background:#359BED;}
 .showpageOf{display:none!important}
#blog-pager .pages{border:none;}

Style 5

#blog-pager{clear:both;margin:30px auto;text-align:center; padding: 7px; }
.blog-pager {background: none;}
.displaypageNum a,.showpage a,.pagecurrent{font-size: 13px;padding: 5px 12px;margin-right:5px; color: #3E5801; background-color:#E0EDC1;}
.displaypageNum a:hover,.showpage a:hover, .pagecurrent{background:#FEF6DF;text-decoration:none;color: #E16800;}
#blog-pager .pagecurrent{font-weight:bold;color: #D25E71;background:#FFDEDF;}
 .showpageOf{display:none!important}
#blog-pager .pages{border:none;}

Style 6

#blog-pager{clear:both;margin:30px auto;text-align:center; padding: 7px; }
.blog-pager {background: none;}
.displaypageNum a,.showpage a,.pagecurrent{font-size: 13px;padding: 5px 12px;margin-right:5px; color: #AD0B00; background-color:#FAB001;}
.displaypageNum a:hover,.showpage a:hover, .pagecurrent{background:#DB4920;text-decoration:none;color: #fff;}
#blog-pager .pagecurrent{font-weight:bold;color: #fff;background:#DB4920;}
 .showpageOf{display:none!important}
#blog-pager .pages{border:none;}

Style 7

#blog-pager{clear:both;margin:30px auto;text-align:center; padding: 7px; }
.blog-pager {background: none;}
.displaypageNum a,.showpage a,.pagecurrent{font-size: 12px;padding: 5px 12px;margin-right:5px; color: #222; background-color:#eee; border: 1px solid #EEEEEE;}
.displaypageNum a:hover,.showpage a:hover, .pagecurrent{background:#E5E5E5;text-decoration:none;color: #222;}
#blog-pager .pagecurrent{font-weight:bold;color: #fff;background:#DB4920;}
 .showpageOf{display:none!important}
#blog-pager .pages{border:none;}

Note: if you want to hide the "First" and "Last" buttons add this line below the CSS code:

.firstpage, .lastpage {display: none;}

2. Adding The Script

Step 4. Now find (CTRL + F) this tag:

</body>

UPDATED! Working version for more than 500 posts:

Step 5. Add the following script just above it:

<b:if cond='data:blog.pageType != &quot;item&quot;'>
<b:if cond='data:blog.pageType != &quot;static_page&quot;'>
<script type='text/javascript'>
  /*<![CDATA[*/
    var perPage=7;
    var numPages=6;
    var firstText ='First';
    var lastText ='Last';
    var prevText ='« Previous';
    var nextText ='Next »';
    var urlactivepage=location.href;
    var home_page="/";
  /*]]>*/
</script>
  <script src="http://helplogger.googlecode.com/svn/trunk/page-navigation2.js"/>
</b:if>
</b:if>

Configuration

After installing, you might want to change these default settings:

perPage: 7,
numPages: 6,
var firstText ='First';
var lastText ='Last';
var prevText ='« Previous';
var nextText ='Next »';
}

1) perPage: how many posts will be shown in each page (7). This value has to be the same as the number of posts on the main page. Otherwise, add the same number by going to "Settings" > "Formatting" and type it in the "Show at most" field, then click on the "Save Settings" button.

2) numPages: how many pages will be shown in the page navigation (6)

3) to replace the 'First', 'Last', "« Previous" and "Next »" texts, just type your own within the quotes.

Labels fix:

By default, Blogger will show 20 posts on label pages. To make this widget appear on label pages, we will have to cut down this down to the value that we gave for the perPage variable.

Find each occurrence of the following code snippet:

expr:href='data:label.url'

Replace it with this one below:

expr:href='data:label.url + "?&amp;max-results=7"'

Here 7 is the number of posts to be displayed per page.

Step 8. Click on the Save Template button and that's it! Enjoy!