Is there a tool to remove unused methods in javascript?

Question

I\'ve got a collection of javascript files from a 3rd party, and I\'d like to remove all the unused methods to get size down to a more reasonable level.

Does anyone

Answer 1

Check out JSCoverage . Generates code coverage statistics that show which lines of a program have been executed (and which have been missed).

Answer 2

Unless the library author kept track of dependencies and provided a way to download the minimal code [e.g. MooTools Core download], it will be hard to to identify 'unused' functions.

The problem is that JS is a dynamic language and there are several ways to call a function.

E.g. you may have a method like

function test() 
{
   //
}

You can call it like

   test();

   var i = 10;
   var hello = i > 1 ? 'test' : 'xyz';

   window[hello]();

Answer 3

No. Because you can "use" methods in insanely dynamic ways like this.

obj[prompt("Gimme a method name.")]();

Answer 4

You'll have to write a perl script. Take no notice of the nay-sayers above.

Such a tool could work with libraries that are designed to only make function calls explicitly. That means no delegates or pointers to functions would be allowed, the use of which in any case only results in unreadable "spaghetti code" and is not best practice. Even if it removes some of these hidden functions you'll discover most if not all of them in testing. The ones you dont discover will be so infrequently used that they will not be worth your time fixing them. Dont obsess with perfection. People go mad doing that.

So applying this one restriction to JavaScript (and libraries) will result in incredible reductions in page size and therefore load times, not to mention readability and maintainability. This is already the case for tools that remove unused CSS such as grunt_CSS and unCSS (see http://addyosmani.com/blog/removing-unused-css/) and which report typical reductions down to one tenth the original size.

Its a win/win situation.

Its noteworthy that all interpreters must address this issue of how to manage self modifying code. For the life of me I dont understand why people want to persist with unrestrained freedom. As noted by Triptych above Javascript functions can be called in ways that are literally "insane". This insane fexibility corrupts the fundamental doctrine of separation of code and data, enables real-time code injection, and invalidates any attempt to maintain code integrity. The result is always unreadable code that is impossible to debug and the side effect to JavaScript - removing the ability to run automatic code pre-optimisation and validation - is much much worse than any possible benefit.

AND - you'd have to feel pretty insecure about your work to want to deliberately obsficate it from both your collegues and yourself. Browser clients that do work extremely well take the "less is more" approach and the best example I've seeen to date is Microsoft Office combination of Access Web Forms paired with SharePoint Access Servcies. The productivity of having a ubiquitous heavy tightly managed runtime interpreter client and its server side clone is absolutely phenomenal.

The future of JavaScript self modifying code technologies therfore is bringing them back into line to respect the...

KISS principle of code and data: Keep It Seperate, Stupid.

Answer 5

I know this is an old question by UglifyJS2 supports removing unused code which may be what you are looking for.

Also worth noting that eslint supports an option called no-unused-vars which actually does some basic handling of detecting if functions are being used or not. It definitely detects it if you make the function anonymous and store it as a variable (but just be aware that as a variable the function declaration doesn't get hoisted immediately)

In the context of detecting unused functions, while extreme, you can consider breaking up a majority of your functions into separate modules because there are packages and tools to help detect unused modules. There is a little segment of sindreshorus's thoughts on tiny modules which might be relevant to that philosophy but that may be extreme for your use case.

Answer 6

I'd like to remove all the unused methods to get size down to a more reasonable level.

There are a couple of tools available:

npm install -g fixmyjs
fixmyjs <filename or folder>

A configurable module that uses JSHint (Github, docs) to flag functions that are unused and perform clean up as well.

I'm not sure that it removes undefined functions as opposed to flagging them. though it is a great tool for cleanup, it appears to lack compatibility with later versions of ECMAScript (more info below).

There is also the Google Closure Compiler which claims to remove dead JS but this is more of a build tool.

Updated

If you are using something like Babel, consider adding ESLint to your text editor, which can trigger a warning on unused methods and even variables and has a --fix CLI option for autofixing some errors and style issues.

I like ESLint because it contains multiple plugins for alternate libs (like React warnings if you're missing a prop), allowing you to catch bugs in advance. They have a solid ecosystem.

As an example: on my NodeJS projects, the config I use is based off of the Airbnb Style Guide.