Return statment not working

the function below is part of a node.js program that i am writing.

 var getDataFromUrl = function(url) {
    rest.get(url).on('complete',function(data) {
        if(data instanceof Error) {
            console.log("url error");
            process.exit(1);
        }else {return data}

        };
    });
};

this function downloads a webpage and returns it content but when i call it in the program it return undefined. how do i solve this problem by the way when called on it own it works fine