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Windows 8 Metro App - How to debug JS that was loaded at runtime

In the last period of time I had to work a lot with JavaScript and not for the UI, but for an entire Metro application on Windows 8. One of the nice features of JavaScript is the ability to access any kind of function and defining or overriding functions at runtime.
This feature is very powerful but also can create a lot of mess. In this moment if we would try to write a C# Metro Application we would not have the ability to load at runtime any kind of assembly or code. The “reflection” part on the .NET framework for Metro Application is not the one that we know from the normal .NET.
In JavaScript if we have a script like this:
(function(){
“use strict”
WinJS.Namespace.define(“MyClass”,{
doSomeAction: function(){
console.warn(“doSomeAction was called”);
}
});
})();
we could evaluate the script at runtime and call or instanced the object and functions that were defined.
The first step is to evaluate the script. Let assume that the definition of this script can be found in a string field named “source”. All we need to do to load this script is to call the “window.execScript” method.
var source = “ our code “;
window.execScript(source);
After this step we can call our classes and functions from our code like this:
MyClass.DoSomeAction();
Wow, very simple. In C# this would not be some simple, but the true is that I would never want to do something like this in C#. Maybe loading an assembly at runtime but this is all that I would like to do.
One big question for you now. How we can debug the code that is loaded dynamically?
You would say that it is not possible. We cannot put a breakpoint in the code that is loaded dynamically. In C# we have a method that stops the code and popup a message to the user to attach a debugger. In JavaScript this is possible using “debugger”. In every place where framework finds a debugger, the execution of code will stop like we would have a breakpoint.
We saw how we can load dynamic code at runtime how we can debug it. This is a powerful feature but be aware. Loading code at runtime is not the best thing do to when we talk about performance. Also a lot of security issues can appear. This can be the tool of devil :-).

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