Object Orientated Programming (OOP) is programming by referring to, well, things.

In regular(linear) programming everything that the program does is laid out by the programmer. In OOP, we have use of objects: self-contained collections of data and instructions.

So, while in linear programming if we wanted to know the length of a string we’d have to construct a loop to count through each of the letters, in OOP we could call up the ‘length’ property of the already-defined string object. The code for counting the letters still exists, but it is inside the string object and the programmer never needs to know how it gets the number. All the programmer needs to know is an what properties an object has, and what it can do: its methods.

What are Properties and Methods? What’s the difference?

The properties of an object are information about it: the colour of a paint or the date of a diary entry would be considered properties of those things. Conversely methods are the things that an object can do: a car can accelerate, an alarm bell can ring.

Let us take, for the purpose of example, a printer:

• Properties

• Paper Left
• Ready Status
• Power Status (on/off)
• Ink Level

• Methods

• Print Single Sided
• Print Double Sided

The Dot Syntax

In many object orientated programming languages the dot syntax is used for referring to objects and their properties and methods. To take the example above, the syntax to refer to the ‘Paper Left’ property would be printer.paperLeft. The syntax for telling it to print a document single-sided would be printer.printSingleSided(myDocument), where myDocument is the document to be printed. Methods always have a pair of brackets at the end, if the method needs information to work then that information is but inside the brackets.

JavaScript Objects

JavaScript is an object orientated language, with its own collection of objects. It also uses the DOM to access objects within HTML files.

The variable is one of the most common JavaScript objects. For a variable containing a string called myString, containing the word “script” there would be properties such as myString.value, which would be “script”, and myString.length, which would be 6. Methods for myString would include toUpperCase(), which converts the letters all to uppercase, and indexOf(), which would give the position of a given letter in the string.

The “text” object corresponds to a HTML . Properties include disabled, which will either be true, in which case the input is disabled, or false, where the input can be activated, and defaultValue, which is the default text in the input. Methods include focus(), which puts the curser in the input, and blur(), which removes the curser from the input.

The “image” object corresponds to a HTML <img /> element. Properties include “src”, the source file of the image, “width” and “hight”. Methods include click(), which has the effect of clicking on the image (for the purposes of an onClick() event, for example).