Data Instances

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

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

let boolean = true;

Math.random()

The Math.random() function returns a floating-point,random number between 0 (inclusive) and 1 (exclusive).

console.log(Math.random()) // 0 - 0.9

Math.floor()

The Math.floor() functions returns largers less than or equal to a given number.

console.log(Math.floor(5.05)); // 5

Single Line Comment

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

// This line will donate a comment

Strings

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

let single = 'Who am I';
let double = "Who am I";

Null

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

let x = null;

Arithmetic Operators

JavaScript support arithmetic operators for:

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

Multi-line Comments

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.

/*
Multi line comment must be
changed before deployment.
*/
let baseUrl = 'https://ajidk.vercel.app/'

Remainder / Modulo Operator

The remainder operator, sometimes called modulo, returns the number that remains after the right-hand number divides into the left-hand number as many times as it evenly can.

// calculates # of weeks in a year, rounds down to
nearest integer.
const weeksInYear = Math.floor(365/7);

// calculates the number of days left over after 365 is
divides by 7
const daysLeftOver = 365 % 7

console.log("A year has " + weeksInYear + " weeks and " 
+ daysLeftOver + " days");

String Interpolation

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

let age = 7

// String concatenation
'Tommy is ' + age + ' years old.'

// String interpolation
`Tommy is ${age} years old.`

Assignment Operators

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
• % module assignment

let number = 100

// Both statements will add 10
number = number + 10
number += 10

console.log(number) // 120

Variables

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.

const currency = '$'
let userIncome = 85000

console.log(currency + userIncome + ' is more than the average income.') // $85000 is more than the average income.

Undefined

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.

var a;

console.log(a) // undefined

Template Literals

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

let name = "Ajidk"
console.log(`Hello, ${name}`) // Hello, Ajidk

console.log(`John is ${10+6} years old.`) // John is 16 years old.

Learn JavaScript: Variables

A variable is a container for data that is stored in computer memory. It is referenced by a descriptive name that a programmer can call to assign a specific value and retrieve it.

// examples of variables
let name = "Tammy"
const found = false
var age = 3
console.log(name, found, age) // Tammy, false, 3

Declaring Variables

To declare a variable in JavaScript, any of these 3 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.

var age;
let weight;
const numberOfFingers = 20;

let Keyword

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.

let count;
console.log(count) // undefined
count = 10;
console.log(count) // 10

const Keyword

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.

const number = 10; 

String Concatenation

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

let service = 'say bismillah bree'
let month = 'May 20th'
let displayText = 'oh my friends ' + service + ' so that life is blessed' + '.'

console.log(displayText) // oh my friend say bismillah bree so that life is blessed.