Why is a Javascript function created with Function constructor unable to access other functions defined outside of it?

Question

See the code below. Why does test2() cause an error while test1() does not? How can the error be avoided (without having to redefine the called function inside the constructor)?

function getRandomInt(min, max) {
        return Math.floor(Math.random() * (max - min + 1)) + min;
    }
var xyz = function (){
                var test1 = function () { getRandomInt(10, 20); };
                test1();  // runs with out problem 
                var test2 = new Function('getRandomInt(10, 20);');
                test2(); //results in "Uncaught ReferenceError: getRandomInt is not defined"
                };

Answer 1

I'm assuming all that is inside another function (an IIFE, maybe?). Code created with new Function is evaluated in the global scope, and it seems getRandomInt is not available there.

Check these demonstrations on jsfiddle: it works if unwrapped, but not inside an IIFE.

If you need the code to be evaluated in the current scope, you have to use eval:

var test2 = eval('(function(){return getRandomInt(10, 20);})');

http://jsfiddle.net/7wPK4/2/

References

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function
• http://www.ecma-international.org/ecma-262/5.1/#sec-15.3.2.1

Answer 2

I found this on MDN:

Functions created with the Function constructor do not create closures to their creation contexts; they always are created in the global scope. When running them, they will only be able to access their own local variables and global ones, not the ones from the scope in which the Function constructor was called. This is different from using eval with code for a function expression.

So maybe your getRandomInt isn't in the global scope? Would need to see the entire code, or a jsFiddle re-creating the problem.