JavaScript is a programming language that powers the dynamic behavior on most websites. Alongside HTML and CSS, it is a core technology that makes the web run.

Methods return information about an object, and are called by appending an instance with a period ., the method name, and parentheses.

Libraries contain methods that can be called by appending the library name with a period ., the method name, and a set of parentheses.

Numbers are a primitive data type. They include the set of all integers and floating point numbers.

The .length property of a string returns the number of characters that make up the string.

When a new piece of data is introduced into a JavaScript program, the program keeps track of it in an instance of that data type. An instance is an individual case of a data type.

Booleans are a primitive data type. They can be either true or false.

The Math.random() function returns a floating-point, random number in the range from 0 (inclusive) up to but not including 1.

The Math.floor() function returns the largest integer less than or equal to the given number.

In JavaScript, single-line comments are created with two consecutive forward slashes //.

Null is a primitive data type. It represents the intentional absence of value. In code, it is represented as null.

Strings are a primitive data type. They are any grouping of characters (letters, spaces, numbers, or symbols) surrounded by single quotes ' or double quotes ".

JavaScript supports arithmetic operators for:

• + addition
• - subtraction
• * multiplication
• / division
• % modulo

In JavaScript, multi-line comments are created by surrounding the lines with /* at the beginning and */ at the end. Comments are good ways for a variety of reasons like explaining a code block or indicating some hints, etc.

An assignment operator assigns a value to its left operand based on the value of its right operand. Here are some of them:

• += addition assignment
• -= subtraction assignment
• *= multiplication assignment
• /= division assignment

String interpolation is the process of evaluating string literals containing one or more placeholders (expressions, variables, etc).

It can be performed using template literals: text ${expression} text.

Variables are used whenever there’s a need to store a piece of data. A variable contains data that can be used in the program elsewhere. Using variables also ensures code re-usability since it can be used to replace the same value in multiple places.

undefined is a primitive JavaScript value that represents lack of defined value. Variables that are declared but not initialized to a value will have the value undefined.

To declare a variable in JavaScript, any of these three keywords can be used along with a variable name:

• var is used in pre-ES6 versions of JavaScript.
• let is the preferred way to declare a variable when it can be reassigned.
• const is the preferred way to declare a variable with a constant value.

Template literals are strings that allow embedded expressions, ${expression}. While regular strings use single ' or double " quotes, template literals use backticks instead.

let creates a local variable in JavaScript & can be re-assigned. Initialization during the declaration of a let variable is optional. A let variable will contain undefined if nothing is assigned to it.

A constant variable can be declared using the keyword const. It must have an assignment. Any attempt of re-assigning a const variable will result in JavaScript runtime error.

In JavaScript, multiple strings can be concatenated together using the + operator. In the example, multiple strings and variables containing string values have been concatenated. After execution of the code block, the displayText variable will contain the concatenated string.