Efficient String Concatenation in JS

In .NET, we use StringBuilder if we need to concatenate strings for better string manipulation performance. For instance,

StringBuilder builder = new StringBuilder();
builder.append("This");
builder.append("is");
builder.append("really");
builder.append("good");
builder.append("for");
builder.append("performance");
  
string str = builder.ToString();

In JS, we can also do the same thing for better memory allocation in string concatenation too.

var builder = new Array();
builder.push("This");
builder.push("is");
builder.push("really");
builder.push("good");
builder.push("for");
builder.push("performance");
 
var str = builder.join("");

This method will perform faster if the number of string concatenation is huge. THe normal += operator will win, otherwise.

Check Efficient JavaScript for more information on optimizing JS code

Debugging JS in VS 2005 using Script Explorer

Breakpoint is one of the useful features available in Visual Studio 2003/2005 to allow developers to trace the current value of variable at the location where the debugger is currently running at. Nevertheless, you can set any breakpoint in the code-behind of the aspx page, but not in declaractive page. No particular client-side javascript function codes can simply be set as breakpoint in Visual Studio.

I rarely debug the client-side JS codes, or I can say NEVER! I have tried to debug it using Script Explorer today and it impressed me. To debug the client-side JavaScript functions, you can use the only-visible-in-debugging-environment Script Explorer in Visual Studio 2003/2005. There are few steps need to be followed:

1. Enable Client-side Script Debugging

IE -> Tools Menu -> Options Menu -> Advanced Tab -> Untick " Disable script debugging check box" in Browsing category.



2. In VS environment, write a simple JS function in external functions.js

function MyLoad(name)
{
   var message = "Welcome, " + name;
   alert(message);            
}

Then, invoke the function in body's load() event in ASPX page.

window.onload = MyLoad("Alvin");

3. Press F5 to debug the page. In debug mode, go to Debug Menu->Windows-> Script Explorer (this option only appears in debug mode). The window of Script Explorer will be shown.



4. Once you debugging the page, you will see list of JS files/resources shown in Script Explorer in tree view.



Double click the "functions.js" and set the breakpoint at particular line. The debugger will stop at that line when it passing through it.




Additionals
If your javascript functions are in the aspx page, you can add breakpoint by

Debug Menu -> "Add Breakpoint" -> "Break At Function" -> type your method name there and choose right language.




Read more in MSDN
1. How to: Debug a Client-Side Script from Microsoft Internet Explorer
2. How to: Enable Client-Side Script Debugging
3. How to: Set a Function Breakpoint


I need a break....