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Here's a requirement from a recent project of mine--I hope you will find the solution interesting and useful:
The easiest way to explain it is by an example which shows you the main points of the code. I've line-numbered the code so it's easy to refer to in the explanation.
In the external file which contains the object type definition:
1 function myObjectType () {
2 if (myObjectType._pcOTinstance)
3 return myObjectType._pcOTinstance;
4 this.property1 = 'a'; // etc.
5 }
6 myObjectType._pcOTinstance = new myObjectType();Line 6 creates an instance as soon as the external JS file is read. I'll explain about myObjectType._pcOTinstance on the next page.
When line 6 calls the constructor, myObjectType._pcOTinstance does
not exist. So the constructor drops through to line 4, initializes the
new instance's properties and returns a reference to it in the normal
way. Hence the code in the external JS file creates one instance
before anything else gets the chance to do so.
When another script uses the constructor, for example
var myInstance = new myObjectType();the property myObjectType._pcOTinstance exists and
the constructor returns a reference to the instance created by
line 6 in the external JS file. No new instance is created--or more
probably an instance is created (with no properties) but then
destroyed immediately because nothing references it.
The line order is very important:
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Created: November 7, 2002
Revised: November 7, 2002
URL: http://webreference.com/programming/javascript/objects/
