// A function that generators a new function for adding numbers
function addGenerator( num ) {

    // Return a simple function for adding two numbers
    // with the first number borrowed from the generator
    return function( toAdd ) {
        return num + toAdd
    };

}

// addFive now contains a function that takes one argument,
// adds five to it, and returns the resulting number
var addFive = addGenerator( 5 );

// We can see here that the result of the addFive function is 9,
// when passed an argument of 4
alert( addFive( 4 ) == 9 );