Creating functions dynamically

[Salvatore]

Hello,

Given an expression f = '2*x+3' from a user input
I would like to do some sort of

function userFunction(x):
return f(x)

is it possible with Javascript ?


Thanks for your advises

Regards

Salvatore

 

[Martin Honnen]

Hello,

Given an expression f = '2*x+3' from a user input
I would like to do some sort of

function userFunction(x):
return f(x)

is it possible with Javascript ?

var fun = new Function("x", f)

 

[Lasse Reichstein Nielsen]

Given an expression f = '2*x+3' from a user input
I would like to do some sort of

function userFunction(x):
return f(x)

is it possible with Javascript ?

This is one of the (very few) cases where you might want to
use the eval function (or the comparable Function constructor).

Just remember that the eval/Function functions understand all
javascript, not just arithmetic expressions, so there is plenty
of rope for a user to hang himself with.

Try this:

var userFunction = Function("x","return ("+f+");");

(by wrapping the value of "f" in "return (...)", you guarantee
that "f" contains an expression, not a full Javascript program.
It doesn't change anything for a determined hacker who wants
to execute arbitrary code, but it catches some accidental
mistypings. Remember: *never* use eval for server-side code!)

/L