Source : https://github.com/Asabeneh/30-Days-Of-JavaScript

(some parts may be modified or removed)

Contents
Data Types (1)
Data Types (2)
- Array
- Date Object

Data Types (1)

Data Types

In the previous section, we mentioned a little bit about data types. Data or values have data types. Data types describe the characteristics of data. Data types can be divided into two:

Primitive data types
Non-primitive data types(Object References)

Primitive Data Types

Primitive data types in JavaScript include:

Numbers - Integers, floats
Strings - Any data under single quote, double quote or backtick quote
Booleans - true or false value
Null - empty value or no value
Undefined - a declared variable without a value
Symbol - A unique value that can be generated by Symbol constructor

Non-primitive data types in JavaScript includes:

Objects
Arrays

Now, let us see what exactly primitive and non-primitive data types mean. Primitive data types are immutable(non-modifiable) data types. Once a primitive data type is created we cannot modify it.

Example:

let word = 'JavaScript'

If we try to modify the string stored in variable word, JavaScript should raise an error. Any data type under a single quote, double quote, or backtick quote is a string data type.

word[0] = 'Y'

This expression does not change the string stored in the variable word. So, we can say that strings are not modifiable or in other words immutable. Primitive data types are compared by its values. Let us compare different data values. See the example below:

let numOne = 3
let numTwo = 3

console.log(numOne == numTwo)      // true

let js = 'JavaScript'
let py = 'Python'

console.log(js == py)             //false 

let lightOn = true
let lightOff = false

console.log(lightOn == lightOff) // false

Non-Primitive Data Types

Non-primitive data types are modifiable or mutable. We can modify the value of non-primitive data types after it gets created. Let us see by creating an array. An array is a list of data values in a square bracket. Arrays can contain the same or different data types. Array values are referenced by their index. In JavaScript array index starts at zero. I.e., the first element of an array is found at index zero, the second element at index one, and the third element at index two, etc.

let nums = [1, 2, 3]
nums[0] = 10

console.log(nums)  // [10, 2, 3]

As you can see, an array, which is a non-primitive data type is mutable. Non-primitive data types cannot be compared by value. Even if two non-primitive data types have the same properties and values, they are not strictly equal.

let nums = [1, 2, 3]
let numbers = [1, 2, 3]

console.log(nums == numbers)  // false

let userOne = {
name:'Asabeneh',
role:'teaching',
country:'Finland'
}

let userTwo = {
name:'Asabeneh',
role:'teaching',
country:'Finland'
}

console.log(userOne == userTwo) // false

Rule of thumb, we do not compare non-primitive data types. Do not compare arrays, functions, or objects. Non-primitive values are referred to as reference types, because they are being compared by reference instead of value. Two objects are only strictly equal if they refer to the same underlying object.

let nums = [1, 2, 3]
let numbers = nums

console.log(nums == numbers)  // true

let userOne = {
name:'Asabeneh',
role:'teaching',
country:'Finland'
}

let userTwo = userOne

console.log(userOne == userTwo)  // true

If you have a hard time understanding the difference between primitive data types and non-primitive data types, you are not the only one. Calm down and just go to the next section and try to come back after some time. Now let us start the data types by number type.

🔝

Numbers

Numbers are integers and decimal values which can do all the arithmetic operations. Let's see some examples of Numbers.

🔝

Declaring Number Data Types

let age = 35
const gravity = 9.81  // we use const for non-changing values, gravitational constant in  m/s2
let mass = 72         // mass in Kilogram
const PI = 3.14       // pi a geometrical constant

// More Examples
const boilingPoint = 100 // temperature in oC, boiling point of water which is a constant
const bodyTemp = 37      // oC average human body temperature, which is a constant

console.log(age, gravity, mass, PI, boilingPoint, bodyTemp)

Math Object

In JavaScript the Math Object provides a lots of methods to work with numbers.

const PI = Math.PI

console.log(PI)                            // 3.141592653589793

// Rounding to the closest number
// if above .5 up if less 0.5 down rounding

console.log(Math.round(PI))                // 3 to round values to the nearest number

console.log(Math.round(9.81))              // 10

console.log(Math.floor(PI))                // 3 rounding down

console.log(Math.ceil(PI))                 // 4 rounding up

console.log(Math.min(-5, 3, 20, 4, 5, 10)) // -5, returns the minimum value

console.log(Math.max(-5, 3, 20, 4, 5, 10)) // 20, returns the maximum value

const randNum = Math.random() // creates random number between 0 to 0.999999
console.log(randNum)

// Let us  create random number between 0 to 10

const num = Math.floor(Math.random () * 11) // creates random number between 0 and 10
console.log(num)

//Absolute value
console.log(Math.abs(-10))      // 10

//Square root
console.log(Math.sqrt(100))     // 10

console.log(Math.sqrt(2))       // 1.4142135623730951

// Power
console.log(Math.pow(3, 2))     // 9

console.log(Math.E)             // 2.718

// Logarithm
// Returns the natural logarithm with base E of x, Math.log(x)
console.log(Math.log(2))        // 0.6931471805599453
console.log(Math.log(10))       // 2.302585092994046

// Returns the natural logarithm of 2 and 10 respectively
console.log(Math.LN2)           // 0.6931471805599453
console.log(Math.LN10)          // 2.302585092994046

// Trigonometry
Math.sin(0)
Math.sin(60)

Math.cos(0)
Math.cos(60)

Random Number Generator

The JavaScript Math Object has a random() method number generator which generates number from 0 to 0.999999999...

let randomNum = Math.random() // generates 0 to 0.999...

Now, let us see how we can use random() method to generate a random number between 0 and 10:

let randomNum = Math.random()         // generates 0 to 0.999
let numBtnZeroAndTen = randomNum * 11

console.log(numBtnZeroAndTen)         // this gives: min 0 and max 10.99

let randomNumRoundToFloor = Math.floor(numBtnZeroAndTen)
console.log(randomNumRoundToFloor)    // this gives between 0 and 10

🔝

Strings

Strings are texts, which are under single , double, back-tick quote. To declare a string, we need a variable name, assignment operator, a value under a single quote, double quote, or backtick quote.

Let's see some examples of strings:

let space = ' '           // an empty space string
let firstName = 'Asabeneh'
let lastName = 'Yetayeh'
let country = 'Finland'
let city = 'Helsinki'
let language = 'JavaScript'
let job = 'teacher'
let quote = "The saying,'Seeing is Believing' is not correct in 2020."
let quotWithBackTick = `The saying,'Seeing is Believing' is not correct in 2020.`

String Concatenation

Connecting two or more strings together is called concatenation. Using the strings declared in the previous String section:

let fullName = firstName + space + lastName; // concatenation, merging two string together.
console.log(fullName);

Asabeneh Yetayeh

We can concatenate strings in different ways.

Concatenating Using Addition Operator

Concatenating using the addition operator is an old way. This way of concatenating is tedious and error-prone. It is good to know how to concatenate this way, but I strongly suggest to use the ES6 template strings (explained later on).

// Declaring different variables of different data types
let space = ' '
let firstName = 'Asabeneh'
let lastName = 'Yetayeh'
let country = 'Finland'
let city = 'Helsinki'
let language = 'JavaScript'
let job = 'teacher'
let age = 250


let fullName =firstName + space + lastName
let personInfoOne = fullName + '. I am ' + age + '. I live in ' + country; // ES5 string addition

console.log(personInfoOne)

Asabeneh Yetayeh. I am 250. I live in Finland

Long Literal Strings (`\`)

A string could be a single character or paragraph or a page. If the string length is too big it does not fit in one line. We can use the backslash character (\) at the end of each line to indicate that the string will continue on the next line.

Example:

const paragraph = "My name is Asabeneh Yetayeh. I live in Finland, Helsinki.\
I am a teacher and I love teaching. I teach HTML, CSS, JavaScript, React, Redux, \
Node.js, Python, Data Analysis and D3.js for anyone who is interested to learn. "

console.log(paragraph)

Escape Sequences in Strings

In JavaScript and other programming languages \ followed by some characters is an escape sequence. Let's see the most common escape characters:

\n: new line
\t: Tab, means 8 spaces
\\: Back slash
': Single quote (')
": Double quote (")

console.log('I hope everyone is enjoying the 30 Days Of JavaScript challenge.\nDo you ?') // line break
console.log('Days\tTopics\tExercises')
console.log('Day 1\t3\t5')
console.log('Day 2\t3\t5')
console.log('Day 3\t3\t5')
console.log('Day 4\t3\t5')
console.log('This is a backslash  symbol (\\)') // To write a backslash
console.log('In every programming language it starts with \"Hello, World!\"')
console.log("In every programming language it starts with \'Hello, World!\'")
console.log('The saying \'Seeing is Believing\' isn\'t correct in 2020')

Output in console:

I hope everyone is enjoying the 30 Days Of JavaScript challenge.
Do you ?
Days  Topics  Exercises
Day 1 3 5
Day 2 3 5
Day 3 3 5
Day 4 3 5
This is a backslash  symbol (\)
In every programming language it starts with "Hello, World!"
In every programming language it starts with 'Hello, World!'
The saying 'Seeing is Believing' isn't correct in 2020

Template Literals (Template Strings)

To create a template strings, we use two back-ticks. We can inject data as expressions inside a template string. To inject data, we enclose the expression with a curly bracket({}) preceded by a $ sign. See the syntax below.

//Syntax
`String template literal text`
`String template literal text ${expression}`

Example: 1

console.log(`The sum of 2 and 3 is 5`)              // statically writing the data
let a = 2
let b = 3
console.log(`The sum of ${a} and ${b} is ${a + b}`) // injecting the data dynamically

Example:2

let firstName = 'Asabeneh'
let lastName = 'Yetayeh'
let country = 'Finland'
let city = 'Helsinki'
let language = 'JavaScript'
let job = 'teacher'
let age = 250
let fullName = firstName + ' ' + lastName

let personInfoTwo = `I am ${fullName}. I am ${age}. I live in ${country}.` //ES6 - String interpolation method
let personInfoThree = `I am ${fullName}. I live in ${city}, ${country}. I am a ${job}. I teach ${language}.`
console.log(personInfoTwo)
console.log(personInfoThree)

I am Asabeneh Yetayeh. I am 250. I live in Finland.
I am Asabeneh Yetayeh. I live in Helsinki, Finland. I am a teacher. I teach JavaScript.

Using a string template or string interpolation method, we can add expressions, which could be a value, or some operations (comparison, arithmetic operations, ternary operation).

let a = 2
let b = 3
console.log(`${a} is greater than ${b}: ${a > b}`)
// ---Output---
// 2 is greater than 3: false

String Methods

Everything in JavaScript is an object. A string is a primitive data type that means we can not modify it once it is created. The string object has many string methods. There are different string methods that can help us to work with strings.

➖ length: The string length method returns the number of characters in a string included empty space.

Example:

let js = 'JavaScript'
console.log(js.length)         // 10
let firstName = 'Asabeneh'
console.log(firstName.length)  // 8

➖ Accessing characters in a string: We can access each character in a string using its index. In programming, counting starts from 0. The first index of the string is zero, and the last index is the length of the string minus one.

Let us access different characters in 'JavaScript' string.

let string = 'JavaScript'
let firstLetter = string[0]

console.log(firstLetter)           // J

let secondLetter = string[1]       // a
let thirdLetter = string[2]
let lastLetter = string[9]

console.log(lastLetter)            // t

let lastIndex = string.length - 1

console.log(lastIndex)  // 9
console.log(string[lastIndex])    // t

--*TBC data types

toUpperCase(): this method changes the string to uppercase letters.

let string = 'JavaScript'

console.log(string.toUpperCase())     // JAVASCRIPT

let firstName = 'Asabeneh'

console.log(firstName.toUpperCase())  // ASABENEH

let country = 'Finland'

console.log(country.toUpperCase())    // FINLAND

toLowerCase(): this method changes the string to lowercase letters.

let string = 'JavasCript'

console.log(string.toLowerCase())     // javascript

let firstName = 'Asabeneh'

console.log(firstName.toLowerCase())  // asabeneh

let country = 'Finland'

console.log(country.toLowerCase())   // finland

substr(): It takes two arguments, the starting index and number of characters to slice.

let string = 'JavaScript'
console.log(string.substr(4,6))    // Script

let country = 'Finland'
console.log(country.substr(3, 4))   // land

substring(): It takes two arguments, the starting index and the stopping index but it doesn't include the character at the stopping index.

let string = 'JavaScript'

console.log(string.substring(0,4))     // Java
console.log(string.substring(4,10))    // Script
console.log(string.substring(4))       // Script

let country = 'Finland'

console.log(country.substring(0, 3))   // Fin
console.log(country.substring(3, 7))   // land
console.log(country.substring(3))      // land

split(): The split method splits a string at a specified place.

let string = '30 Days Of JavaScript'

console.log(string.split())     // Changes to an array -> ["30 Days Of JavaScript"]
console.log(string.split(' '))  // Split to an array at space -> ["30", "Days", "Of", "JavaScript"]

let firstName = 'Asabeneh'

console.log(firstName.split())    // Change to an array - > ["Asabeneh"]
console.log(firstName.split(''))  // Split to an array at each letter ->  ["A", "s", "a", "b", "e", "n", "e", "h"]

let countries = 'Finland, Sweden, Norway, Denmark, and Iceland'

console.log(countries.split(','))  // split to any array at comma -> ["Finland", " Sweden", " Norway", " Denmark", " and Iceland"]
console.log(countries.split(', ')) //  ["Finland", "Sweden", "Norway", "Denmark", "and Iceland"]

trim(): Removes trailing space in the beginning or the end of a string.

let string = '   30 Days Of JavaScript   '

console.log(string)
console.log(string.trim(' '))

let firstName = ' Asabeneh '

console.log(firstName)
console.log(firstName.trim())  // still removes spaces at the beginning and the end of the string

   30 Days Of JavasCript   
30 Days Of JavasCript
  Asabeneh 
Asabeneh

includes(): It takes a substring argument and it checks if substring argument exists in the string. includes() returns a boolean. If a substring exist in a string, it returns true, otherwise it returns false.

let string = '30 Days Of JavaScript'

console.log(string.includes('Days'))     // true
console.log(string.includes('days'))     // false - it is case sensitive!
console.log(string.includes('Script'))   // true
console.log(string.includes('script'))   // false
console.log(string.includes('java'))     // false
console.log(string.includes('Java'))     // true

let country = 'Finland'

console.log(country.includes('fin'))     // false
console.log(country.includes('Fin'))     // true
console.log(country.includes('land'))    // true
console.log(country.includes('Land'))    // false

replace(): takes as a parameter the old substring and a new substring.

string.replace(oldsubstring, newsubstring)

let string = '30 Days Of JavaScript'
console.log(string.replace('JavaScript', 'Python')) // 30 Days Of Python

let country = 'Finland'
console.log(country.replace('Fin', 'Noman'))       // Nomanland

charAt(): Takes index and it returns the value at that index

string.charAt(index)

let string = '30 Days Of JavaScript'
console.log(string.charAt(0))        // 3

let lastIndex = string.length - 1
console.log(string.charAt(lastIndex)) // t

charCodeAt(): Takes index and it returns char code (ASCII number) of the value at that index

string.charCodeAt(index)

let string = '30 Days Of JavaScript'
console.log(string.charCodeAt(3))        // D ASCII number is 68

let lastIndex = string.length - 1
console.log(string.charCodeAt(lastIndex)) // t ASCII is 116

indexOf(): Takes a substring and if the substring exists in a string it returns the first position of the substring if does not exist it returns -1

string.indexOf(substring)

let string = '30 Days Of JavaScript'

console.log(string.indexOf('D'))          // 3
console.log(string.indexOf('Days'))       // 3
console.log(string.indexOf('days'))       // -1
console.log(string.indexOf('a'))          // 4
console.log(string.indexOf('JavaScript')) // 11
console.log(string.indexOf('Script'))     //15
console.log(string.indexOf('script'))     // -1

lastIndexOf(): Takes a substring and if the substring exists in a string it returns the last position of the substring if it does not exist it returns -1

//syntax
string.lastIndexOf(substring)

let string = 'I love JavaScript. If you do not love JavaScript what else can you love.'

console.log(string.lastIndexOf('love'))       // 67
console.log(string.lastIndexOf('you'))        // 63
console.log(string.lastIndexOf('JavaScript')) // 38

concat(): it takes many substrings and joins them.

string.concat(substring, substring, substring)

let string = '30'
console.log(string.concat("Days", "Of", "JavaScript")) // 30DaysOfJavaScript

let country = 'Fin'
console.log(country.concat("land")) // Finland

startsWith: it takes a substring as an argument and it checks if the string starts with that specified substring. It returns a boolean(true or false).

//syntax
string.startsWith(substring)

let string = 'Love is the best to in this world'

console.log(string.startsWith('Love'))   // true
console.log(string.startsWith('love'))   // false
console.log(string.startsWith('world'))  // false

let country = 'Finland'

console.log(country.startsWith('Fin'))   // true
console.log(country.startsWith('fin'))   // false
console.log(country.startsWith('land'))  //  false

endsWith: it takes a substring as an argument and it checks if the string ends with that specified substring. It returns a boolean(true or false).

string.endsWith(substring)

let string = 'Love is the most powerful feeling in the world'

console.log(string.endsWith('world'))         // true
console.log(string.endsWith('love'))          // false
console.log(string.endsWith('in the world')) // true

let country = 'Finland'

console.log(country.endsWith('land'))         // true
console.log(country.endsWith('fin'))          // false
console.log(country.endsWith('Fin'))          //  false

search: it takes a substring as an argument and it returns the index of the first match. The search value can be a string or a regular expression pattern.

string.search(substring)

let string = 'I love JavaScript. If you do not love JavaScript what else can you love.'
console.log(string.search('love'))          // 2
console.log(string.search(/javascript/gi))  // 7

match: it takes a substring or regular expression pattern as an argument and it returns an array if there is match if not it returns null. Let us see how a regular expression pattern looks like. It starts with / sign and ends with / sign.

let string = 'love'
let patternOne = /love/     // with out any flag
let patternTwo = /love/gi   // g-means to search in the whole text, i - case insensitive

Match syntax

// syntax
string.match(substring)

let string = 'I love JavaScript. If you do not love JavaScript what else can you love.'
console.log(string.match('love'))

["love", index: 2, input: "I love JavaScript. If you do not love JavaScript what else can you love.", groups: undefined]

let pattern = /love/gi
console.log(string.match(pattern))   // ["love", "love", "love"]

Let us extract numbers from text using a regular expression. This is not the regular expression section, do not panic! We will cover regular expressions later on.

let txt = 'In 2019, I ran 30 Days of Python. Now, in 2020 I am super exited to start this challenge'
let regEx = /\d+/

// d with escape character means d not a normal d instead acts a digit
// + means one or more digit numbers,
// if there is g after that it means global, search everywhere.

console.log(txt.match(regEx))  // ["2", "0", "1", "9", "3", "0", "2", "0", "2", "0"]
console.log(txt.match(/\d+/g)) // ["2019", "30", "2020"]

repeat(): it takes a number as argument and it returns the repeated version of the string.

string.repeat(n)

let string = 'love'
console.log(string.repeat(10)) // lovelovelovelovelovelovelovelovelovelove

🔝

Checking Data Types and Casting

Checking Data Types

To check the data type of a certain variable we use the typeof method.

Example:

// Different javascript data types
// Let's declare different data types

let firstName = 'Asabeneh'      // string
let lastName = 'Yetayeh'        // string
let country = 'Finland'         // string
let city = 'Helsinki'           // string
let age = 250                   // number, it is not my real age, do not worry about it
let job                         // undefined, because a value was not assigned

console.log(typeof 'Asabeneh')  // string
console.log(typeof firstName)   // string
console.log(typeof 10)          // number
console.log(typeof 3.14)        // number
console.log(typeof true)        // boolean
console.log(typeof false)       // boolean
console.log(typeof NaN)         // number
console.log(typeof job)         // undefined
console.log(typeof undefined)   // undefined
console.log(typeof null)        // object

Changing Data Type (Casting)

Casting: Converting one data type to another data type. We use parseInt(), parseFloat(), Number(), + sign, str() When we do arithmetic operations string numbers should be first converted to integer or float if not it returns an error.

String to Int

We can convert string number to a number. Any number inside a quote is a string number. An example of a string number: '10', '5', etc. We can convert string to number using the following methods:

parseInt()
Number()
Plus sign(+)

let num = '10'
let numInt = parseInt(num)
console.log(numInt) // 10

let num = '10'
let numInt = Number(num)

console.log(numInt) // 10

let num = '10'
let numInt = +num

console.log(numInt) // 10

String to Float

We can convert string float number to a float number. Any float number inside a quote is a string float number. An example of a string float number: '9.81', '3.14', '1.44', etc. We can convert string float to number using the following methods:

parseFloat()
Number()
Plus sign(+)

let num = '9.81'
let numFloat = parseFloat(num)

console.log(numFloat) // 9.81

let num = '9.81'
let numFloat = Number(num)

console.log(numFloat) // 9.81

let num = '9.81'
let numFloat = +num

console.log(numFloat) // 9.81

Float to Int

We can convert float numbers to integers. We use the following method to convert float to int:

parseInt()

let num = 9.81
let numInt = parseInt(num)

console.log(numInt) // 9

🌕 You are awesome. You have just completed day 2 challenges and you are two steps ahead on your way to greatness. Now do some exercises for your brain and for your muscle.

🔝

Booleans

A boolean data type represents one of the two values:true or false. Boolean value is either true or false. The use of these data types will be clear when you start the comparison operator. Any comparisons return a boolean value which is either true or false.

Example: Boolean Values

let isLightOn = true
let isRaining = false
let isHungry = false
let isMarried = true
let truValue = 4 > 3    // true
let falseValue = 4 < 3  // false

We agreed that boolean values are either true or false.

Truthy values

All numbers(positive and negative) are truthy except zero
All strings are truthy except an empty string ('')
The boolean true

Falsy values

0
0n
null
undefined
NaN
the boolean false
'', "", ``, empty string

It is good to remember those truthy values and falsy values. In later section, we will use them with conditions to make decisions.

🔝

Undefined

If we declare a variable and if we do not assign a value, the value will be undefined. In addition to this, if a function is not returning the value, it will be undefined.

let firstName
console.log(firstName) //not defined, because it is not assigned to a value yet

Null

let empty = null
console.log(empty) // -> null , means no value

🔝

Data Types (2)

Array

Creating Array

let arr = Array()
// or new Array()

// This the most recommended way to create an empty list
let arr = []

const numbers = [0, 3.14, 9.81, 37, 98.6, 100] // array of numbers
const fruits = ['banana', 'orange', 'mango', 'lemon'] // array of strings, fruits

const arr = [
    'Asabeneh',
    250,
    true,
    { country: 'Finland', city: 'Helsinki' },
    { skills: ['HTML', 'CSS', 'JS', 'React', 'Python'] }
] // arr containing different data types

Creating array using split

let companiesString = 'Facebook, Google, Microsoft, Apple, IBM, Oracle, Amazon'
const companies = companiesString.split(',')

console.log(companies) // ["Facebook", " Google", " Microsoft", " Apple", " IBM", " Oracle", " Amazon"]


let js = 'JavaScript'
const charsInJavaScript = js.split('')

console.log(charsInJavaScript) // ["J", "a", "v", "a", "S", "c", "r", "i", "p", "t"]

✏ you can split with white space also.

Methods to manipulate array

Array

Array(8) : // it creates an array sized 8

fill(myPrimValue)

fill all the array elements with a static value

const eight0values = Array(8).fill(0) // it creates eight element values filled with '0'
console.log(eight0values) // [0, 0, 0, 0, 0, 0, 0, 0]

length

arrayIdentifier.length --> lenght is a identifier

indexOf(checkValue)

it returns index value of the check value.

lastIndexOf(checkValue)

it returns index value of the check value reversely. (tersten sırasını verir)

includes(checkValue) : returns boolean

Array.isArray(identifierName)

slice(delimiterValue)

it slice according to delimiter value.

toString()

converts array to string comma delimited.

join()

it returns comma joined values of the array

join(delimiterValue) : different delimiter can be used.

myArray.join("#");

concat(anotherArray)

combines arrays.

slice() : cut out an array

it doesnt include the ending position.

slice()  // -> all items
slice(0) // -> all items
slice(0,myArray.length) // -> all item
slice(1,4) // -> slice [2,3,4]

splice

Syntax

myArray.splice(lnStartPos,numOfItems,itemsToAdd);

Exs:

const numbers = [1, 2, 3, 4, 5]
numbers.splice()
console.log(numbers)                // -> remove all items

const numbers = [1, 2, 3, 4, 5]
numbers.splice(0,1)
console.log(numbers)            // remove the first item

const numbers = [1, 2, 3, 4, 5, 6]
numbers.splice(3, 3, 7, 8, 9)
console.log(numbers.splice(3, 3, 7, 8, 9))  // -> [1, 2, 3, 7, 8, 9] //it removes three item and replace three items

push(myValue)

adding item in the end.

pop(myValue)

Removing item in the end.

shift()

Removing one array element in the beginning of the array.

const numbers = [1, 2, 3, 4, 5]
numbers.shift() // -> remove one item from the beginning
console.log(numbers) // -> [2,3,4,5]

unshift

Adding array element in the beginning of the array.

const numbers = [1, 2, 3, 4, 5]
numbers.unshift(0) // -> add one item from the beginning
console.log(numbers) // -> [0,1,2,3,4,5]

reverse()

reverse the order of an array.

const numbers = [1, 2, 3, 4, 5]
numbers.reverse() // -> reverse array order
console.log(numbers) // [5, 4, 3, 2, 1]

sort

const webTechs = [
  'HTML',
  'CSS',
  'JavaScript',
  'React',
  'Redux',
  'Node',
  'MongoDB'
]

webTechs.sort()
console.log(webTechs) // ["CSS", "HTML", "JavaScript", "MongoDB", "Node", "React", "Redux"]

webTechs.reverse() // after sorting we can reverse it
console.log(webTechs) // ["Redux", "React", "Node", "MongoDB", "JavaScript", "HTML", "CSS"]

sorting with a callback function later.

Array of Arrays

const firstNums = [1, 2, 3]
const secondNums = [1, 4, 9]

const arrayOfArray =  [[1, 2, 3], [1, 2, 3]]
console.log(arrayOfArray[0]) // [1, 2, 3]

🔝

Date Object

Time is an important thing. We like to know the time a certain activity or event. In JavaScript current time and date is created using JavaScript Date Object. The object we create using Date object provides many methods to work with date and time.The methods we use to get date and time information from a date object values are started with a word get because it provide the information.

getFullYear(), getMonth(), getDate(), getDay(), getHours(), getMinutes, getSeconds(), getMilliseconds(), getTime(), getDay()

Creating a time object

Once we create time object. The time object will provide information about time. Let us create a time object

const now = new Date()
console.log(now) // Sat Jan 04 2020 00:56:41 GMT+0200 (Eastern European Standard Time)

We have created a time object and we can access any date time information from the object using the get methods we have mentioned on the table.

Getting full year

Let's extract or get the full year from a time object.

const now = new Date()
console.log(now.getFullYear()) // 2020

Getting month

Let's extract or get the month from a time object.

const now = new Date()
console.log(now.getMonth()) // 0, because the month is January,  month(0-11)

Getting date

Let's extract or get the date of the month from a time object.

const now = new Date()
console.log(now.getDate()) // 4, because the day of the month is 4th,  day(1-31)

Getting day

Let's extract or get the day of the week from a time object.

const now = new Date()
console.log(now.getDay()) // 6, because the day is Saturday which is the 7th day
//  Sunday is 0, Monday is 1 and Saturday is 6
// Getting the weekday as a number (0-6)

Getting hours

Let's extract or get the hours from a time object.

const now = new Date()
console.log(now.getHours()) // 0, because the time is 00:56:41

Getting minutes

Let's extract or get the minutes from a time object.

const now = new Date()
console.log(now.getMinutes()) // 56, because the time is 00:56:41

Getting seconds

Let's extract or get the seconds from a time object.

const now = new Date()
console.log(now.getSeconds()) // 41, because the time is 00:56:41

Getting time

This method give time in milliseconds starting from January 1, 1970. It is also know as Unix time. We can get the unix time in two ways:

Using getTime()

const now = new Date() //
console.log(now.getTime()) // 1578092201341, this is the number of seconds passed from January 1, 1970 to January 4, 2020 00:56:41

Using Date.now()

const allSeconds = Date.now() //
console.log(allSeconds) // 1578092201341, this is the number of seconds passed from January 1, 1970 to January 4, 2020 00:56:41

const timeInSeconds = new Date().getTime()
console.log(allSeconds == timeInSeconds) // true

Let us format these values to a human readable time format. Example:

const now = new Date()
const year = now.getFullYear() // return year
const month = now.getMonth() + 1 // return month(0 - 11)
const date = now.getDate() // return date (1 - 31)
const hours = now.getHours() // return number (0 - 23)
const minutes = now.getMinutes() // return number (0 -59)

console.log(`${date}/${month}/${year} ${hours}:${minutes}`) // 4/1/2020 0:56

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Contents

Data Types (1)

Data Types

Primitive Data Types

Non-Primitive Data Types

Numbers

Declaring Number Data Types

Math Object

Random Number Generator

Strings

String Concatenation

Concatenating Using Addition Operator

Long Literal Strings (\)

Escape Sequences in Strings

Template Literals (Template Strings)

String Methods

Checking Data Types and Casting

Checking Data Types

Changing Data Type (Casting)

String to Int

String to Float

Float to Int

Booleans

Truthy values

Falsy values

Undefined

Null

Data Types (2)

Array

Creating Array

Methods to manipulate array

Array

fill(myPrimValue)

length

indexOf(checkValue)

lastIndexOf(checkValue)

includes(checkValue) : returns boolean

Array.isArray(identifierName)

slice(delimiterValue)

toString()

join()

concat(anotherArray)

slice() : cut out an array

splice

push(myValue)

pop(myValue)

shift()

unshift

reverse()

sort

Array of Arrays

Date Object

Creating a time object

Getting full year

Getting month

Getting date

Getting day

Getting hours

Getting minutes

Getting seconds

Getting time

Long Literal Strings (`\`)