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

JavaScript libraries contain methods that you can call by appending the library name with a period (.), the method name, and a set of parentheses.

The console.log() method is used to log or print text to the console. It can also be used to print objects, arrays, and other info. This makes it a useful tool for debugging JavaScript.

Numbers are a primitive data type, one of the most basic data types available within the JavaScript language. 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 you introduce a new piece of data 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, one of the most basic types in JavaScript. They can be either true or false. Use Boolean() to evaluate the truth value.

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

The Math.floor() function in JavaScript returns the largest integer less than or equal to the given number. In the above example , console.log(Math.floor(number)) will log 15 in console when the number variable is set to the value 15.95 .

In JavaScript, single-line comments are made with two consecutive forward slashes (//).

Null is a primitive data type, one of the most basic data types available within the JavaScript language. 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 the basic arithmetic operators for addition (+), subtraction (-), multiplication (*), and division (/).

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

In JavaScript, the addition assignment operator (+=) can be used to add the value on the right hand side to the existing value & assign it to the variable. The addition assignment operator is a shorthand for variableName = variableName + value. Subtraction assignment (-=), multiplication assignment (*=) & division assignment (/=) perform similar operations.

String interpolation is the process of evaluating string literals containing one or more placeholders (expressions, variables, etc). The two main ways to interpolate strings are with string concatenation (syntax: "string" + expression + "string") or template literals (syntax: `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 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.

Whenever there’s a need to use a piece of data, variables are a good solution. A variable contains data that can be used in the program. For instance, if a certain code block is written to check the age, the value to be compared can be assigned in a variable. The best practice for JavaScript variables is to give them names that identify their use.

To declare a variable in JavaScript, any of these three keywords - var, let or const can be used along with a variable name.

In JavaScript, template literals are strings that allow embedded expressions (${expression}). While regular strings use single (') or double (") quotes, template literals use backticks instead. Take a look at the code block above to see examples.

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. In the code block, a const named numberOfColumns has been assigned the value 4. It is a one-time assignment . Any attempt of re-assigning a const variable will result in JavaScript runtime error: TypeError: Assignment to constant variable. Variables defined with the keyword const must be assigned values during declaration.

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.