Side effect free features

Question

Creating an online math tutorial, I want users on my site to define (math) functions that, by definition, are free from side effects. The easiest way to achieve this is to do the following

// ... get string entered by user and store it in variable user_code
// now build function
var user_function = eval ("(function (x) { return (" + user_code + "); })");

If users log in x*x, it user_functionwill contain a function that calculates the square of its argument.

Now this opens my page for cross-site scripting and malicious code.

Is there a way to avoid this other than writing the expression parser myself? In other words, I want to allow the execution of functions in a well-defined context, for example, without a function that accesses global variables.

Answer 1

, , javascript, ?

, - math.js, ..