Modern Javascript Development: constructors and objects

26Feb/081

Modern Javascript Development: constructors and objects

JavaScript doesn't have a "class" keyword or any formal class construct. Instead, functions are 1st class objects. When you write a function, you are essentially writing a constructor for a new object.
Here we are defining a object constructor called "newClass" and assigning some member values.

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function newClass() {
this.name = "newClass";
this.options = {size:42};
};
var myInstance = new newClass();
alert(myInstance.name);
alert(myInstance.options.size);

You can also specify arguments for the constructor just like any other function and assign the argument values to the objects members.

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function newClassInitialzed(name, options) {
this.name = name;
this.options = options;
};
var anotherInstance = new newClassInitialzed("John", {size:42})
alert(anotherInstance.name);
alert(anotherInstance.options.size);

So what happens if you don't want to pass the name and options to the constructor every time? You can specify defaults for the member variables values using the logical OR ( || ) operator in JavaScript. The logical OR operator has a short-circuit which always returns "true" if the first argument is true.

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