JavaScript and Open Data

4Objects and Prototypes

JavaScript distinguishes itself from most usual “object-oriented programming” (OOP) languages, which are “class based”: JavaScript is “prototype based”. This originality is confusing for people accustomed to other OOP languages, and sometimes perceived as a weakness vis-à-vis better “controlled” languages such as Java, of which it “inherited” the name based on a misunderstanding.

4.1. Introduction

This chapter is organized as follows:

• – an introduction about the notions of “concept” versus “named entities” should help in understanding the difference between “class-based” and “prototype-based” OOP;
• – section 4.2: This section details the syntax and use of the “object literal” in JavaScript, popular through the JSON format, which is widely used to exchange data over the Internet;
• – section 4.3: This section deals with the methods of the built-in objects “Object” and “Object.prototype”, how they provide the notion of inheritance by delegation and how objects can be related;
• – section 4.4: After analyzing the role of prototypes, we detail the three approaches for creating objects:
  • - literal: this includes the operator {..}, the role of the functions Object and Function, to enlighten the role of the “prototypes” in the inheritance mechanism in JavaScript,
  • - prototypal: this includes the innovative methods Object.create and Object.assign (ES6),
  • - classical: this consists of the operator “new” and the “constructor” functions.

We can hardly talk about objects ...