Question

I need to make sure that some submitted code has a function named mapfn defined, and that that function returns a result. I came up with the following regex expression:
mapfn\s+?\=\s+?function\s+?\(split\)\s+?\{.+?return\(result\).+?\} which matches something like

mapfn = function (split) {
    var i = 5+4;
    for (var j = 0; j < 10; j++) {
        i += j*Math.random()*10;
    }
    var result = i;
    return(result)
}

Which is desirable but if I go to for an example closure compiler with this code and get something like mapfn=function(){for(var b=9,a=0;a<10;a++)b+=a*Math.random()*10;return b};, that regex is useless. Also, the user submits something like

function mapfn (split) {
    var i = 5+4;
    for (var j = 0; j < 10; j++) {
        i += j*Math.random()*10;
    }
    var result = i;
    return(result)
}

Then the regex is also useless.

I feel there’s a more elegant solution for this problem than having 5 or 6 regular expressions for this job and trying to match any one of them.

Answer 1

This is totally impossible to do with a regex.

Consider

function x() { if (1 < 0) return 7; }

All you can do is parse the function in a Javascript environment, call it, and see what it returns.

If you want to make sure that it always returns a value, you’ll need to solve the Halting Problem.