Why javascript frameworks like backbone as we have ASP.Net MVC, Ajax and partial rendering
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What is the need of Backbone.js and handlebars, because what we are doing in the Asp.net MVC is done here, but the problem is if we have lot of javascipt code in the project it will be hard to maintain and find errors, and more over we don’t have intellisense for javascript as we have in C# or other language.

And Javascript errors are more difficult to find, in javascript we didn't get any compile time errors even though the code is wrong, but in languages like C# we will get compile time error if code got some syntax error
And Javascript is not type safe for example an Array can contain any object(employee, customer and etc).
OOPS is not that much friendly, not interface concepts.
No call stack and etc …

Never seen javascript errors are logged in some persistence area.

i do understand it runs on client side and performance will be better to some extent, but I hope the same can be achieved using asp.net MVC. i am not opposing Javascript but want to understand the rationale behind these frameworks growing more nowadays