Given a string describing a Javascript function, convert it to a Javascript function

Question

Say I've got a Javascript string like the following

var fnStr = "function(){blah1;blah2;blah3; }" ; 

(This may be from an expression the user has typed in, duly sanitized, or it may be the result of some symbolic computation. It really doesn't matter).

I want to define fn as if the following line was in my code:

var fn = function(){blah1;blah2;blah3; } ; 

How do I do that?

The best I've come up with is the following:

var fn = eval("var f = function(){ return "+fnStr+";}; f() ;") ; 

This seems to do the trick, even though it uses the dreaded eval(), and uses a slightly convoluted argument. Can I do better? I.e. either not use eval(), or supply it with a simpler argument?

Answer 1

There's also the Function object.

var adder = new Function("a", "b", "return a + b");