Understanding JavaScript: Basics and Fundamentals

JavaScript is a high-level, interpreted programming language that is primarily used to enhance web pages to provide for a more user-friendly experience. It is a key pillar of modern web development and forms the foundation for frameworks like React. This unit will cover the basics and fundamentals of JavaScript.

Introduction to JavaScript

JavaScript was initially created to “make web pages alive”. Today, JavaScript can execute not only in the browser, but also on the server, or actually on any device where exists a special program called the JavaScript engine.

Variables and Data Types

In JavaScript, there are several types of data that we can work with:

• Numbers: Both integers and floating-point numbers are supported.
• Strings: A string in JavaScript must be surrounded by quotes.
• Boolean: This type only has two values: true and false.
• Null: This type has only one value: null.
• Undefined: A variable that has been declared but has not been assigned a value, is undefined.
• Objects: These are complex data structures that can hold different types of data.

Variables are "containers" for storing data values. In JavaScript, there are three types of variables you can declare:

• var: This is the most common way to declare a variable.
• let: This allows you to declare variables that are limited to the scope of a block statement.
• const: This allows you to declare variables whose values are never intended to change.

Operators and Control Flow

JavaScript includes arithmetic operators like addition (+), subtraction (-), multiplication (*), and division (/). It also includes the modulus operator (%) to find the remainder of division and the increment (++) and decrement (--) operators.

Control flow is the order in which the computer executes statements in a script. Control flow statements in JavaScript include:

• if...else: This is used to perform different actions based on different conditions.
• switch: This selects one of many code blocks to be executed.
• for loop: This loops through a block of code a number of times.
• while loop: This loops through a block of code while a specified condition is true.

Functions and Scope

A JavaScript function is a block of code designed to perform a particular task. Functions are executed when they are called. This is known as invoking a function. Functions can be defined using function declaration or function expression.

Scope determines the accessibility or visibility of variables, functions, and objects in some particular part of your code during runtime. In other words, scope controls the visibility and lifetimes of variables and parameters.

Arrays and Objects

An array is a special variable, which can hold more than one value at a time. Arrays are list-like objects whose prototype has methods to perform traversal and mutation operations.

Objects in JavaScript, just as in many other programming languages, can be compared to objects in real life. In JavaScript, an object is a standalone entity, with properties and type.

Introduction to ES6 features

ES6, also known as ECMAScript 2015, introduced many changes to JavaScript. Some of the most notable features include:

• Arrow functions: These provide a new way to declare functions.
• Classes: JavaScript classes provide a much simpler and clearer syntax to create objects and deal with inheritance.
• Promises: Promises are used to handle asynchronous operations in JavaScript.
• Template literals: Template literals are string literals allowing embedded expressions.

By the end of this unit, you should have a solid understanding of the basics of JavaScript, which will serve as a foundation for the rest of the course.