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 piler 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.

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 piler 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.

• javascript
• regex
• function

2 Answers 2

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.

SLaks is right, but you don't need to invoke the halting problem to prove it's impossible with regular expressions. With a regular expression, you can't even tell whether a JavaScript function contains return used as a keyword even if you could match curly brackets to tell where a definition function ends.

Consider

function () {
  1 /[/**/]; return 1 ///
}

vs

function () {
    /[/**/]; return 1 ///  
}

The first contains a return because it is equivalent to

function () {
  1 / [];
  return 1;
  ///
}

but the second does not because it is equivalent to

function () {
  new RegExp("[\\/\\*\\*\\/]; return 1 ");
  //
}

There can be arbitrarily many characters between the /* and */ so you need to pletely disambiguate the first / to tell whether it is a division operator or a regular expression to tell whether the keyword return occurs in the function. That requires a full parse, and JavaScript does not have a regular lexical grammar.