vl - inheritance

Overview of Object Oriented Programming

• Key concept: Inheritance

  • Grouping features and reusing code.

  • Analogy: Children inheriting traits from parents.

  • Example: A programmer inherits characteristics of a person and adds more.

Inheritance in JavaScript

• Multiple methods of achieving inheritance.

• Focus on the default method:

  • Called prototype chaining.

  • Concept: Setting the prototype to a particular object for behavior and property inheritance.

Prototype Chaining

• Setting the prototype involves:

  • Inheriting all behaviors and properties from the specified prototype object.

Overriding Methods

• Example: Overriding the toString method.

  • Specific implementation provided to avoid defaulting back to the prototype's implementation.

  • toString now returns the name property of the object.

Shape Examples

• Defined shapes:

  • Function Shape:

  • Has a property called name.

  • Overrides the toString method to return its name.

  • 2D Shape:

  • No override of toString; inherits it from Shape.

  • Triangle Shape:

  • Takes parameters side and height.

  • Properties and behaviors added to represent a triangle.

Inheritance Implementation

• Procedure for making 2D Shape inherit from Shape:

  • Set the prototype of 2D Shape to the Shape object.

  • Use constructor new 2D Shape to create an instance.

  • Results in inheritance of the toString method from Shape.

Prototype Chain Behavior

• Explanation of how prototype chain checks work:

  • First checks the current object (e.g., 2D Shape).

  • If property not found, checks the prototype (e.g., Shape).

  • Retrieves name property if it belongs to the Shape prototype.

Triangle Instance Creation

• Creating an instance of Triangle:

  • Example given for instantiation.

  • States the potential for using prototype properties/methods.

Moving Properties to Prototypes

• Guidelines on when to move properties to a prototype:

  • Typical creation of object with constructor function uses this to add own properties.

  • Each instance has its own property, which consumes memory.

Memory Efficiency

• Key factor: If properties have the same value across instances, move property to the prototype.

  • Example: If every shape has the same name, it is inefficient to have unique instances.

  • Instead, define the property on the prototype: Shape.prototype.name = 'shape';

Shared Values

• Aim to share values to save memory:

  • Properties should be defined on prototype when shared by all instances.

• Methods should be generally defined on prototype for shared access between object instances.

• Properties defined within the constructor using this when unique to instances.

Conclusion

• Summary of concepts covered related to inheritance in JavaScript.

• Reinforces efficiency of using prototype for shared properties and benefits of object-oriented design principles.

• Closing remarks for further engagement in the next session.