The toString() method returns a string representing the source code of the function.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe...

That's pretty neat. Thanks for the link.

If called on a Function it returns the source of the function, which allows for all sorts of meta programming.

If memory serves, a real world example was Angular doing a toString then injecting dependencies before calling eval on the new code.

To be honest, I don’t know that there’s ever a good reason to use it in production as it almost always involves performance and security problems.

> involves performance [...] problems

Except when it solves them! https://mrale.ph/blog/2018/02/03/maybe-you-dont-need-rust-to...

I once used it for a proof of concept for computer worm type message on a sort of message board. Used to re-generate the source code to be added to new messages.

Yep. We used to use this for some hacks back before AST libraries were a thing, mainly because Function.prototype.toString() preserves comments.

function foo() { /* a comment! / }

console.log(foo.toString()); //-> "function foo() { / a comment! */ }"