INHERITANCE

The concept most often discussed in relation to OO programming is inheritance. Many OO languages support two types of inheritance: interface inheritance, where only the method signatures are inherited, and implementation inheritance, where actual methods are inherited. Interface inheritance is not possible in ECMAScript because functions do not have signatures. Implementation inheritance is the only type of inheritance supported by ECMAScript, and this is done primarily through the use of prototype chaining.

Prototype Chaining

ECMA-262 describes prototype chaining as the primary method of inheritance in ECMAScript. The basic idea is to use the concept of prototypes to inherit properties and methods between two reference types. Recall the relationship between constructors, prototypes, and instances: each constructor has a prototype object that points back to the constructor, and instances have an internal pointer to the prototype. What if the prototype were actually an instance...