Form Validation with JavaScript - Object Lessons
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Before we get into object construction, a quick primer is in order, for all of you who are new to the weird and wonderful world of objects.
In JavaScript, an "object" is simply a set of program statements which perform a specific task; they lay down the basic rules for an object, specifying what it can and cannot do. A typical object constructor contains both variables and functions, and serves as the template from which to spawn specific instances of that object.
Every object constructed from the template has certain characteristics, or "properties," and certain pre-defined functions, or "methods." These properties and methods of the object correspond directly with the variables and functions within the object definition.
Once an object has been defined, JavaScript allows you to spawn as many instances of the object as you like. Each of these instances is a completely independent object, with its own properties and methods, and can thus be manipulated independently of other objects.
Now, you're probably wondering whether this is a little redundant, since JavaScript also allows you to create your own functions and use them wherever required in your code. And you're correct, to some extent; if you're only planning to spawn a single object, a function will work just as well.
But there are situations where you need to spawn more than one instance of an object - for example, multiple menu trees, multiple image swaps, or multiple ticker tapes. In such a situation, objects are preferred, since each instance comes with its own variables and functions, and thus can be manipulated without affecting other variables within the program.
Objects also help you keep your code modular - you can define an object constructor in a separate file, and include that file only in the pages where you plan to use the object - and simplify code changes, since you only need to edit a single file to add new functionality to all your spawned objects.
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