Higher Order Programming is the ability to use functions as values. So you can pass functions as arguments to other functions and functions can be the return value of other functions. This style of programming is mostly used in functional programming, but it can also be very useful in 'regular' object oriented programming. A good example of this is the Ruby Scripting Language, which combines all the advantages of pure object oriented programming and higher order programming. Sadly, Ruby is not supported by any browser, so it cannot be used for websites. We are lucky however that Javascript is available in every browser, and that Javascript is so flexible that it can be extended to make higher order programming a helpful tool in scripting webpages.

The sort method

Most people will know Javascript only as a scripting language that makes image switching and annoying popup windows possible. However the Javascript implementations hint at the more advanced programming possibilities through the sort Method of arrays. In it's simple form sort() will just sort the array: The code document.write([2,3,1,4].sort()) will write "1,2,3,4". But the sort method can do more. It allows a compare function as an optional argument. That's higher order programming right there. Suppose we have an array of objects. Each object has a date property, and we want to sort the objects by their date value:

arrayOfObjects.sort(

  function (x,y) {

    return x.date-y.date;

  }

);

The compare function is called regularly during sorting. It must return a negative value when x comes before y, zero when the are equal and a possitive value when x comes after y. This is exactly what substraction does for numbers and dates, for strings you can just use < and >.