How to expand nested function?

[MAGNETO903]

I have 2 simple functions, for example:
f1(x) = 2*x
f2(x) = x^2

And one complex function:
f3(x) = f1(f2(x))

Can I using mathjs expand function f3?
I need to get something like this:

math.expand("f3(x)") // return 2*x^2

or

math.simplify(math.parse("f3(x)")) // should return 2*x^2

Can I do this?

[josdejong]

That is an interesting one. There is no functionality built in for this, but I think you could build it quite easily.

After parsing an expression like f1(x), you could transform the parsed expression and replace all occurrences of f1 with it's implementation 2*x using the method .transform(...). When replacing, you should make sure the function variables should be correctly renamed too when needed, such that f1(y) will be replaced with 2*y.

See docs: https://mathjs.org/docs/expressions/expression_trees.html