JavaScript syntax
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Objects
For convenience, types are normally subdivided into primitives and objects. Objects are entities that have an identity (they are only equal to themselves) and that map property names to values ("slots" in prototype-based programming terminology). Objects may be thought of as associative arrays or hashes, and are often implemented using these data structures. However, objects have additional features, such as a prototype chain, which ordinary associative arrays do not have.
JavaScript has several kinds of built-in objects, namely Array, Boolean, Date, Function, Math, Number, Object, RegExp and String. Other objects are "host objects", defined not by the language, but by the runtime environment. For example, in a browser, typical host objects belong to the DOM (window, form, links, etc.).
Creating objects
Objects can be created using a constructor or an object literal. The constructor can use either a built-in Object function or a custom function. It is a convention that constructor functions are given a name that starts with a capital letter:
// Constructor
const anObject = new Object();
// Object literal
const objectA = {};
const objectA2 = {}; // A != A2, {}s create new objects as copies.
const objectB = {index1: 'value 1', index2: 'value 2'};
// Custom constructor (see below)
Object literals and array literals allow one to easily create flexible data structures:
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