Create JavaScript Function Dynamically

function createFunction (name, args, body) {
    var argumentsLength = arguments.length
        , name
        , args
        , body
        , isString = function (element) {return Object.prototype.toString.call(element) === '[object String]';};
    if (argumentsLength === 0) {
        name = '';
        args = '';
        body = '';
    } else if (argumentsLength === 1) {
        name = name;
        args = '';
        body = '';
        if (!isString(name)) {throw new Error('Function name must be a string.');}
    } else if (argumentsLength === 2) {
        name = name;
        body = args;
        args = '';
        if (!isString(name)) {throw new Error('Function name must be a string.');}
        if (!isString(body)) {throw new Error('Function body must be a string.');}
    } else if (argumentsLength === 3) {
        name = name;
        args = args;
        body = body;
        if (!isString(name)) {throw new Error('Function name must be a string.');}
        if (!isString(args)) {throw new Error('Function arguments must be a string.');}
        if (!isString(args)) {throw new Error('Function body must be a string.');}
    }
    return (new Function('return function ' + name + ' (' + args + ') {' + body + '};'))();
}

var func = createFunction ();
console.log(func.toString());
console.log(func());

var func = createFunction ('a');
console.log(func.toString());
console.log(func());

var func = createFunction ('a', 'return 1;');
console.log(func.toString());
console.log(func());

var func = createFunction ('a', 'b, c', 'return b + c;');
console.log(func.toString());
console.log(func(2, 3));