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Photo of Tanzim Saqib Tanzim Saqib is a Senior Developer, who spent half of his life on software and worked for many companies like #1 .NET controls provider Telerik Inc, #1 personalized Web 2.0 start-page like Pageflakes (acquired by LiveUniverse). He developed many projects ranging from banking solutions for Citibank, HSBC, Wamu, Wells Fargo etc. to Paperless Virtual University. He is industry's earliest and leading widget developer and as know as "Widget Master" to his peers.

He is a preacher of Microsoft technologies. While he jams with the latest additions to .NET, in his spare time he blogs at http://weblogs.asp.net/TanzimSaqib, maintains his personal website http://www.TanzimSaqib.com, leads .NET Research group. writes articles.

He is an easy going, fun loving, and passionate technology individual who is open to any kind of business opportunity and professional relationship. He currently lives in Bangladesh, but travels anywhere in the world on professional demand.

Email: me at TanzimSaqib dot com

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It's a very common bad practice. We often iterate through array, build HTML contents and keep on concatenating into certain DOM element. Every time you execute the block of code under the loop, you create the HTML markups, discover a div, access the innerHTML of a div, and for += operator you again discover the same div, access its innerHTML and concatenate it before assigning. function pageLoad() { var links = ["microsoft.com", "tanzimsaqib.com", "asp.net"]; $get('divContent').innerHTML = 'The following ......

While we develop AJAX applications, we often carelessly ignore giving up bad practices, which cause effects which are not so significantly visible when the site is not so large in volume. But, it’s often severe performance issue when it is the case for sites that make heavy use of AJAX technologies such as Pageflakes, NetVibes etc. There are so many AJAX widgets in one page that little memory leak issues combined may even result the site crash into very nasty “Operation aborted”. There are a lot ......

Don't you think the following block of code has written keeping every possible good practice in mind? Any option for performance improvement?function pageLoad() { var stringArray = new Array(); // Suppose there're a lot of strings in the array like: stringArray.push('<div&g... stringArray.push('some content'); stringArray.push('</div&... // ... code edited to save space var veryLongHtml = $get('divContent').innerHTML; var count = stringArray.length; for(var i=0; i<count; ++i) veryLongHtml ......

Take a look at the following loop. This loop calls a function in each iteration and the function does some stuffs. Can you think of any performance improvement idea?for(var i=0; i<count; ++i) processElement(elements[i]); Well, for sufficiently large array, function delegates may result in significant performance improvement to the loop.var delegate = processElement; for(var i=0; i<count; ++i) delegate(elements[i]); The reason behind performance improvement is, JavaScript interpreter will use ......

We have seen DOM caching before and function delegation is also a kind of function caching. Take a look at the following snippet: for(var i=0; i<count; ++i) $get('divContent').appendCh... As you can figure out the code is going to be something like: var divContent = $get('divContent'); for(var i=0; i<count; ++i) divContent.appendChild(elem... That is fine, but you can also cache browser function like appendChild. So, the ultimate optimization will be like the following: ......

Unlike .NET languages or any other compiler languages, JavaScript interpreter can not optimize switch block. Especially when switch statement is used with different types of data, it's a heavy operation for the browser due to conversion operations occur in consequences, it's an elegant way of decision branching though.


In one of my earlier posts, I talked about DOM element accessing in a loop but forgot to talk about a very common, yet performance issue in AJAX. We often use code like the following:var items = []; // Suppose a very long array for(var i=0; i<items.length; ++i) ; // Some actionsIt can be a severe performance issue if the array is so large. JavaScript is an interpreted language, so when interpreter executes code line by line, every time it checks the condition inside the loop, you end up accessing ......

It's not pretty common. But, if you ever encounter such code, be sure it's a very bad practice. Introducing more scopes is a performance issue for JavaScript interpreter. It adds a new scope in the ladder. See the following sample scope:function pageLoad() { scope1(); function scope1() { alert('scope1'); scope2(); function scope2() { alert('scope2'); } } } Introducing more scopes enforces the interpreter to go through new more sections in the scope chain that it maintains for code execution. So, ......

Avoid implementing your own getElementById method that will cause script to DOM marshalling overhead. Each time you traverse the DOM and look for certain HTML element requires the JavaScript interpreter to marshalling script to DOM. It's always better to use getElementById of document object. So, before you write a function, make sure similar functionality can be achieved from some other built-in functions.


When a webpage loads, it fetches the stylesheets, javascript, images, other objects etc. So, when it is done, it's already late and user may complain about the site's poor speed of execution. One way you can make it faster, you can start JavaScript execution immediately right after the HTML DOM has finished loading and ready to traverse, before the images. // Introduce our custom event onDOMReady window.onDOMReady = DOMReady function DOMReady(fn) { // According to standard implementation if(document.addEventListener) ......

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