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
1. Primitive data types
2. Non-primitive data types(Object References)
### Primitive Data Types
Primitive data types in JavaScript includes:
1. Numbers - Integers, floats
2. Strings - Any data under single or double quote
3. Booleans - true or false value
4. Null - empty value or no value
5. Undefined - a declared variable without a value
Non-primitive data types in JavaScript includes:
1. Objects
2. Functions
3. Arrays
Now, let us see what exactly mean primitive and non-primitive data types.
*Primitive* data types are immutable(non-modifiable) data types. Once a primitive data type is created we can not modify it.
**Example:**
```js
let word = 'JavaScript'
```
If we try to modify the string stored in variable *word*, JavaScript will raise an error. Any data type under a single quote, double-quote, or backtick is a string data type.
```js
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 immutable.
Primitive data types are compared by its values. Let us compare different data values. See the example below:
```js
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.
```js
let nums = [1, 2, 3]
nums[0] = 10
console.log(nums) // [10, 2, 3]
```
As you can see, an array in which a non-primitive data type is mutable. Non-primitive data types can not be compared by value. Even if two non-primitive data types have the same properties and values, they are not strictly equal.
```js
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)
```
Rule of thumb, we do not compare non-primitive data types. Do not compare array, function, or object.
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.
```js
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.
Lets' see some examples of Numbers.
### Declaring number data types
```js
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
In JavaScript the Math Object provides a lots of methods to work with numbers.
```js
const PI = Math.PI
console.log(PI) // 3.141592653589793
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 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 of base E of x, Math.log(x)
console.log(Math.log(2)) // 0.6931471805599453
console.log(Math.log(10)) // 2.302585092994046
// Trigonometry
Math.sin(0)
Math.sin(60)
Math.cos(0)
Math.cos(60)
```
## Strings
Strings are texts, which are under **_single_** or **_double_** quote. To declare a string, we need a variable name, assignment operator, a value under a single quote, double-quote, or backtick.
Lets' see some examples of string:
```js
let space = ' ' // an empty space string
let firstName = 'Asabeneh'
let lastName = 'Yetayeh'
let country = 'Finland'
let city = 'Helsinki'
let language = 'JavaScript'
let job = 'teacher'
```
### String Concatenation
Connect two or more strings together is called concatenation.
```js
// 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'
```
```js
let fullName = firstName + space + lastName; // concatenation, merging two string together.
console.log(fullName);
```
```sh
// out
Asabeneh Yetayeh
```
We can concatenate string 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 second way.
```js
// 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
console.log(personInfoOne)
```
```sh
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:**
```js
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. \
In the end of 2019, I was thinking to expand my teaching and to reach \
to global audience and I started a Python challenge from November 20 - December 19.\
It was one of the most rewarding and inspiring experience.\
Now, we are in 2020. I am enjoying preparing the 30DaysOfJavaScript challenge and \
I hope you are enjoying too."
console.log(paragraph)
```
#### Escape Sequences in string
In JavaScript and other programming language \ 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 (")
```js
console.log('I hope every one 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 back slash symbol (\\)') // To write a back slash
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\' is\'t correct in 2020')
```
#### Template Literals(Template Strings)
To create a template string, we use two backticks. We can inject data as expression inside a template string. To inject data, we enclose the expression with a curly bracket({}) followed by a $ sign. See the syntax below.
```js
//Syntax
`String literal text`
`String literal text ${expression}`
```
**Example: 1**
```js
console.log(`The sum of 2 and 3 is 5`)
let a = 2
let b = 3
console.log(`The sum of ${a} and ${b} is ${a + b}`)
```
**Example:2**
```js
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 ${language}.`
console.log(personInfoTwo)
console.log(personInfoThree)
```
```sh
I am Asabeneh Yetayeh. I am 250. I live in Finland.
I am Asabeneh Yetayeh. I live in Helsinki, Finland. I am a teacher. I teach JavaScript.
```
Using a string template or string interpolation method, we can add expression, which could be a value or some operations(comparison, arithmetic operations, ternary operation).
```js
let a = 2
let b = 3
console.log(`${a} is greater than ${b}: ${a > b}`)
```
```sh
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 once it is created. The string object has many string methods. There are different string methods that can help us to work with strings.
1.*length*: The string *length* method returns the number of characters in a string included empty space.
**Example:**
```js
let js = 'JavaScript'
console.log(js.length) // 10
let firstName = 'Asabeneh'
console.log(firstName.length) // 8
```
2.*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 one minus the length of the string.
8.*trim()*: Removes trailing space in the beginning or the end of a string.
```js
let string = ' 30 Days Of JavaScript '
console.log(string)
console.log(string.trim(' ')) //
let firstName = ' Asabeneh '
console.log(firstName)
console.log(firstName.trim()) //
```
```sh
30 Days Of JavasCript
30 Days Of JavasCript
Asabeneh
Asabeneh
```
9.*includes()*: It takes a substring argument and it check if substring argument exists in the string. *includes()* returns a boolean. It checks if a substring exist in a string and it returns true if it exists and false if it doesn't exist.
```js
let string = '30 Days Of JavaScript'
console.log(string.includes('Days')) // true
console.log(string.includes('days')) // false
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
```
10.*replace()*: takes to parameter the old substring and new substring.
```js
string.replace(oldsubstring, newsubstring)
```
```js
let string = '30 Days Of JavaScript'
console.log(string.replace('JavaScript', 'Python')) // 30 Days Of Python
11.*charAt()*: Takes index and it returns the value at that index
```js
string.charAt(index)
```
```js
let string = '30 Days Of JavaScript'
console.log(string.charAt(0)) // 3
let lastIndex = string.length - 1
console.log(string.charAt(lastIndex)) // t
```
12.*charCodeAt()*: Takes index and it returns char code(ASCII number) of the value at that index
```js
string.charCodeAt(index)
```
```js
let string = '30 Days Of JavaScript'
console.log(string.charCodeAt(3)) // D ASCII number is 51
let lastIndex = string.length - 1
console.log(string.charCodeAt(lastIndex)) // t ASCII is 116
```
13.*indexOf()*: Takes 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
```js
string.indexOf(substring)
```
```js
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
```
14.*lastIndexOf()*: Takes 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
```js
string.lastIndexOf(index)
```
```js
let string = 'I love JavaScript. If you do not love JavaScript what else can you love.'
16.*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).
```js
//syntax
string.startsWith(substring)
```
```js
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
```
17.*endsWith*: 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).
```js
string.endsWith(substring)
```
```js
let string = 'Love is the best to in this world'
console.log(string.endsWith('world')) // true
console.log(string.endsWith('love')) // false
console.log(string.endsWith('in this world')) // true
let country = 'Finland'
console.log(country.endsWith('land')) // true
console.log(country.endsWith('fin')) // false
console.log(country.endsWith('Fin')) // false
```
18.*search*: it takes a substring as an argument and it returns the index of the first match.
```js
string.search(substring)
```
```js
let string = 'I love JavaScript. If you do not love JavaScript what else can you love.'
console.log(string.search('love')) // 2
```
19.*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.
```js
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
```
```js
string.match(substring)
```
```js
let string = 'I love JavaScript. If you do not love JavaScript what else can you love.'
console.log(string.match('love')) //
/*
output
["love", index: 2, input: "I love JavaScript. If you do not love JavaScript what else can you love.", groups: undefined]
1. Declare a variable name challenge and assign it to an initial value **'30 Days Of JavaScript'**.
2. Print the string on the browser console using __console.log()__
3. Print the __length__ of the string on the browser console using _console.log()_
4. Change all the string to capital letters using __toUpperCase()__ method
5. Change all the string to lowercase letters using __toLowerCase()__ method
6. Cut(slice) out the first word of the string using __substr()__ or __substring()__ method
7. Slice out the phrase *Days Of JavaScript* from *30 Days Of JavaScript*.
8. Use __substr__ to slice out the phase __because because because__ in the following sentence:__'You cannot end a sentence with because because because is a conjunction'__
9. Check if the string contains a word __Script__ using __includes()__ method
10. Split the __string__ into __array__ using __split()__ method
11. Split the string 30 Days Of JavaScript at the space using __split()__ method
12. 'Facebook, Google, Microsoft, Apple, IBM, Oracle, Amazon' __split__ the string at the comma and change it to an array.
13. Change 30 Days Of JavaScript to 30 Days Of Python using __replace()__ method.
14. What is character at index 15 in '30 Days Of JavaScript' string use __charAt()__ method.
15. What is the character code of J in '30 Days Of JavaScript' string using __charCodeAt()__
16. Use __indexOf__ to determine the position of the first occurrence of a in 30 Days Of JavaScript
17. Use __lastIndexOf__ to determine the position of the last occurrence of a in 30 Days Of JavaScript.
18. Use __indexOf__ to find the position of the first occurrence of the word __because__ in the following sentence:__'You cannot end a sentence with because because because is a conjunction'__
19. Use __lastIndexOf__ to find the position of the last occurrence of the word __because__ in the following sentence:__'You cannot end a sentence with because because because is a conjunction'__
20. Use __search__ to find the position of the first occurrence of the word __because__ in the following sentence:__'You cannot end a sentence with because because because is a conjunction'__
21. Use __trim()__ to remove if there is trailing whitespace at the beginning and the end of a string.E.g ' 30 Days Of JavaScript '.
22. Use __startsWith()__ method with the string *30 Days Of JavaScript* make the result true
23. Use __endsWith()__ method with the string *30 Days Of JavaScript* make the result true
24. Use __match()__ method to find all the a’s in 30 Days Of JavaScript
25. Use __match()__ to count the number all because's in the following sentence:__'You cannot end a sentence with because because because is a conjunction'__
26. Use __concat()__ and merge '30 Days of' and 'JavaScript' to a single string, '30 Days Of JavaScript'
27. Use __repeat()__ method to print 30 Days Of JavaScript 2 times
28. Love is the best thing in this world. Some found their love and some are still looking for their love. Count the number of word love in this sentence.
29. Calculate the total annual income of the person by extract the numbers from the following text. 'He earns 5000 euro from salary per month, 10000 euro annual bonus, 15000 euro online courses per month.'
30. Clean the following text and find the most frequent word(hint, use replace and regular express).
```js
const sentence = '%I $am@% a %tea@cher%, &and& I lo%#ve %tea@ching%;. There $is nothing; &as& mo@re rewarding as educa@ting &and&@emp%o@wering peo@ple. ;I found tea@ching m%o@re interesting tha@n any other %jo@bs. %Do@es thi%s mo@tivate yo@u to be a tea@cher!? %Th#is 30#Days&OfJavaScript &is also $the $result of &love& of tea&ching'
```
31. Using console.log() print out the following statement.
```sh
The quote 'There is no exercise better for the heart than reaching down and lifting people up.' by John Holmes teaches us to help to one another.
```
32. Using console.log() print out the following quote by Mother Teresa.
```sh
"Love is not patronizing and charity isn't about pity, it is about love. Charity and love are the same -- with charity you give love, so don't just give money but reach out your hand instead."
