Glossary

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Definition

Below we have briefly explained some terms you may need to gain a deeper understanding of the JavaScript language and related terms and to grasp the concepts. Please do not forget to read in detail by following the link after reading the short summary.

If you think something is wrong or missing here, feel free to correct it.

Most explanations and documentation are from MDN Web Docs (opens in a new tab).

Definitions or terms

Types

Primitive

In JavaScript, a primitive (primitive value, primitive data type) is data that is not an object and has no methods or properties. Click here (opens in a new tab)

Copy

Shallow copy

Shallow copy is copying the reference of an object or an array to a new variable. This only assigns a new variable to the reference of the original object, which means that the two variables share the same memory address. Therefore, changes made to one variable affect the other. Click here (opens in a new tab)

Deep copy

Deep copy, on the other hand, involves copying the entire original object. This includes all of the object's properties and sub-properties, such as nested objects and arrays. As a result, the two variables have different memory addresses, and changes made to one variable do not affect the other. Click here (opens in a new tab)

Interchangeability principle

Mutable

A mutable value is one that can be changed without creating an entirely new value. In JavaScript, objects and arrays are mutable by default, but primitive values are not — once a primitive value is created, it cannot be changed, although the variable that holds it may be reassigned. Click here (opens in a new tab)

Immutable

An immutable value is one whose content cannot be changed without creating an entirely new value. Click here (opens in a new tab)

JavaScript

Built-in objects

Array

The Array object, as with arrays in other programming languages, enables storing a collection of multiple items under a single variable name, and has members for performing common array operations. Click here (opens in a new tab)

Object

The Object type represents one of JavaScript's data types. It is used to store various keyed collections and more complex entities. Objects can be created using the Object() constructor or the object initializer / literal syntax. Click here (opens in a new tab)

JavaScript Object Notation

JSON (JavaScript Object Notation) is an open standard data format used for exchanging data between humans and computers. It is designed to represent structured data using key-value pairs and is often used to represent data in the form of JavaScript objects and arrays. JSON is widely supported by many programming languages because it is platform-independent, and it is also easy for humans to read and understand. Click here (opens in a new tab)