Deleting JavaScript Properties and Methods

The investigation here will say whether we can delete the property or method in the constructor function. This is the constructor function we have:

function ObjectType()

{

this.propertyType1 = "Yes type one";

this.methodType1 = functionType1;

}

We shall see if we can delete a property or method in a constructor function. We start with the property. Replace the statements in the investigate() function with the following:

answer = delete ObjectType.propertyType1;

alert('Boolean result is ' + answer );

alert(ObjectType.propertyType1); //try the property

Note that we have now used the ObjectType class and not the theObject derived object. Our aim is to delete the property from the object type and not from a derived object.

I tested the code with the five browsers; the Boolean result was true, meaning that the property was deleted. After deleting, the value of the property displayed was undefined. This confirmed that the property was deleted.

Let us see if the method can be deleted. Replace the statements in the investigate() function with the following:

answer = delete ObjectType.methodType1;

alert('Boolean result is ' + answer );

ObjectType.methodType1(); //try the property

When I tested the code with the five browsers, the Boolean result was true, meaning that the method was deleted. After deleting, the method was tried and nothing happened. This confirmed that the method was deleted.

So you can delete properties and methods of the constructor function.

Note: when you are deleting a method, you do not need the attached () brackets. The following expression does not need the () brackets:

delete ObjectType.methodType1

You attach the () brackets when you are calling the method.

This is a summary of what we've discovered:

• A property or method that belongs to an object can be deleted.

• When you add any property or method to the object type, you can delete the property or method with the assigned value of any of the derived objects.

• You can delete the property or the method we add to the object type when null is assigned to the property or method.

• You can delete a property or a method of the constructor function.

Wow, we have gotten ourselves into web research; the results clarify what we can do.

Use of Deleting Properties

An area in programming where you will have to delete a property is when you have an object that behaves like an array (e.g. an array itself or a database query result).

Let us take a break here. In the next and last part of the series, we shall see how to add properties and methods at run time. We shall see how the user can indirectly give a property or method to an object. See you in the next part of the series.