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.
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