**Congratulations** for deciding to participate in a 30 days of JavaScript programming challenge . In this challenge you will learn everything you need to be a JavaScript programmer and in general the whole concepts of programming. In the end of the challenge you will get a 30DaysOfJavaScript programming challenge certificate. Join the [telegram group](https://t.me/ThirtyDaysOfJavaScript).
**A 30DaysOfJavaScript** challenge is a guide for both beginners and advanced JavaScript developers. Welcome to JavaScript. I enjoy using and teaching JavaScript and I hope you will do so. JavaScript is the language of the browser.
In this step by step tutorial, you will learn JavaScript, the most popular programming language in the history of mankind.
You use JavaScript **_to add interactivity to websites, to develop mobile apps, desktop applications, games_** and nowadays JavaScript can be used for **_machine learning_** and **_AI_**.
**_JavaScript (JS)_** has increased in popularity in recent years and has been the leading
programming language for four consecutive years and is the most used programming language on
Github.
# Requirements
No prior knowledge of programming is required to follow this challenge. You need only:
Install [google chrome](https://www.google.com/chrome/) if you do not have one yet. We can write small JavaScript code on the browser console but we do not use the browser console to develop applications.
After you open the google chrome console try to explore the marked buttons. We will spend most of the time on the Console part. The Console is the place where your JavaScript code goes. The google console V8 engine change your JavaScript code to machine code.
Let us write a JavaScript code on google chrome console:
### Writing Code on browser Console
We can write any JavaScript code on google console or any browser console but for this challenge we only focus on google chrome console. Open the console using:
To write our first JavaScript code we used a builtin function **console.log()**. We passed an argument as an input data and the function display the output. We passed 'Hello, World' as input data or argument in the console.log() function.
As you can see from the above snippet code, *console.log()* can take multiple arguments.
Congratulations! You wrote your first JavaScript code using *console.log()*.
#### Comment
We add comment to our code. Comment is very important to make code more readable and to leave remark in our code. JavaScript does not execute comment part of our code. Any text starts with // in JavaScript is a comment or any thing enclose like this /* */ is a comment.
Example: Single Line Comment
// This is the first comment
// This is the second comment
// I am a single line comment
Example: Multiline Comment
/*
This is a multiline comment
multiline comment take multiple lines.
JavaScript is the language the langauge of the web.
*/
#### Syntax
JavaScript is a programming language and it has its own syntax like other languages. If we do not write a syntax which JavaScript understands it will raise different kind of errors. We will see different kind of JavaScript errors later but for now let us see syntax error.
I made a deliberate mistake the console raise a syntax error. Actually, the syntax is very informative. It tell what kind of mistake we made and we can fix the by reading error feedback. The process of identifying and removing errors from a program is called debugging. Let us fix the errors:
So far, we saw how to display text using a *console.log()*. If we are printing text or string using *console.log()*, the text has to be under single, double or back tick.
We can write code on the browser console but it won't be for a big project. In real work environment, developers use different code editors to write codes. In this 30 days python JavaScript challenge we will use visual studio code.
Visual studio code is a very popular open source text editor and I would recommend to [download](https://code.visualstudio.com/) visual studio code, but if you are in favor of other editors, feel free to follow with what you have.
If you installed visual studio code, let us start using it.
### How to use visual studio code
Open the visual studio code by double clicking the visual studio icon. When you open it you will get this kind of interface. Try to interact with the labelled icons.
JavaScript can be added to a web page in three ways:
- **_Inline script_**
- **_Internal script_**
- **_External script_**
- **_Multiple External scripts_**
The following sections show different ways of adding JavaScript code to your web page.
## Inline Script
Create a folder on your desktop and call it 30DaysOfJS or in any location and create an **_index.html_** file in project folder. Then paste the following code and open it in a browser, either in [Chrome](https://www.google.com/chrome/).
```html
<!DOCTYPE html>
<html>
<head>
<title>30DaysOfScript:Inline Script</title>
</head>
<body>
<buttononclick="alert('Welcome to 30DaysOfJavaScript!');">Click Me</button>
</body>
</html>
```
Now, you wrote your first inline script. We can create a pop up alert message using the build in *alert()* function.
## Internal script
Internal script can be written in the _head_ or the _body_ but it is preferred to put it on the body of the html document.
This is how we write internal script most of the time. Writing the JavaScript code in the body section is the most preferred place. Open the browser console to see the out put from the console.log()
First we should create an external JavaScript file with .js extension. Any JavaScript file ends with .js. Create a file introduction.js inside your project directory and write the following code and link this. js file at the bottom of the body
In JavaScript and also other programming languages there are different kinds of data types. The following are JavaScript primitive data types:_String, Number, Boolean, undefined, Null_ and _Symbol_.
## Number
- Integer: Integer(negative, zero and positive) numbers
Example:
... -3, -2, -1, 0, 1, 2, 3 ...
- Float: Decimal number
Example
... -3.5, -2.25, -1.0, 0.0, 1.1, 2.2, 3.5 ...
## String
A collection of one or more characters under a single quote , double quote or back stick.
**Example:**
```js
'Asabeneh'
'Finland'
'JavaScript is a beautiful programming language'
"I love teaching"
'I hope you are enjoying the first day'
`We can also create a string using a back tick`
```
## Booleans
Boolean value is either true or false. Any comparisons return a boolean value which is either true or false.
A boolean data type is either a True or False value.
In JavaScript if we don't assign a value to a variable the value is undefined. In addition to that if a function is not returning anything it returns undefined.
```js
let firstName;
console.log(firstName); //not defined, because it is not assigned to a value yet
Variables are _containers_ of data. Variables _store_ data in a memory location. When a variable is declared a memory location is reserved and when it is assigned to a value, the memory space will be filled with that data. To declare a variable we use, _var_, _let_ or _const_ keywords. I will talk about var, let and const in detail in other section(scope). For now, the above explanation is enough.
For a variable which changes at different time we use _let_ but if the data doesn't change at all we use _const_. For example PI, country name, gravity do no change and we can use *const*.
A JavaScript variable name shouldn't begin with a number
A JavaScript variable name does not allow special characters except dollar sign and underscore.
Let's declare variables with different data types. To declare a variable we need let or const keyword, the name of the variable, an equal sign (assignment operator) and a value.
In the previous section, we mentioned a little bit about data types. Data have data types. Data types describe the characteristics of data. Data types can be divided into
1. Primitive data types
2. Non-primitive data types(Object References)
Primitive data types in JavaScript includes:
1. Numbers
2. Strings
3. Booleans
4. Null
5. Undefined
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 single quote, double quote or back tick 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 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 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. Array is a list of data values in a square bracket. Array can contain the same or different data types. Arrays values are referenced by its index which starts at zero.
```js
let nums = [1, 2, 3]
nums[0] = 10
console.log(nums) // [10, 2, 3]
```
As you can see, an array which a non-primitive data type is a 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 hard time to understand 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 text 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 back tick.
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 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
```
### Template Literals(Template Strings)
To create a template string we use back two back ticks. We can inject data as expression inside a template string. To inject data we enclose the expression with curly bracket({}) followed by $ sign. See the syntax blow.
```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 ${language}.`
console.log(personInfoTwo)
console.log(personInfoThree)
```
```sh
I am Asabeneh Yetayeh. I am 250. I live in Finland.
I am Asabeneh Yetayeh. I live in Helsinki, Finland. I am a teacher. I teach JavaScript.
```
Using string template or string interpolation method we can add expression which could be a value or some operations(comparison, arithmetic operations, ternary operation)
```js
let a = 2
let b = 3
console.log(`${a} is greater than ${b}: ${a > b}`)
```
```sh
2 is greater than 3: false
```
## String Methods
Everything in JavaScript is an object. String is a primitive data type that means we can not modify once it is created. String object has many string methods. There many string methods which 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 characters 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
Let us access the first character in 'JavaScript' string.
```js
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
```
3.*toUpperCase()*: this method changes the string to uppercase letters.
```js
let string = 'JavaScript'
console.log(string.toUpperCase()) // JAVASCRIPT
let firstName = 'Asabeneh'
console.log(firstName.toUpperCase()) // ASABENEH
let country = 'Finland'
console.log(country.toUpperCase()) // FINLAND
```
4.*toLowerCase()*: this method changes the string to lowercase letters.
```js
let string = 'JavasCript'
console.log(string.toLowerCase()) // javascript
let firstName = 'Asabeneh'
console.log(firstName.toLowerCase()) // asabeneh
let country = 'Finland'
console.log(country.toLowerCase()) // finland
```
5.*substr()*: It takes two arguments,the starting index and number of characters to slice.
```js
let string = 'JavaScript'
console.log(string.substr(4,6) // Script
let country = 'Finland'
console.log(country.substr(3, 4)) // land
```
6.*substring()*: It takes two arguments,the starting index and the stopping index but it doesn't include the stopping index.
```js
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
```
7. *split(): The split method splits a string at a specified place.
```js
let string = '30 Days Of JavaScipt'
console.log(string.split()) // ["30 Days Of JavaScript"]
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.charCodeAt(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
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.serch(substring)
```
```js
let string = 'I love JavaScript. If you do not love JavaScript what else can you love.'
console.log(string.search('love')) // 2
```
1.*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 expresson 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]
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**
```js
let isLightOn = true;
let isRaining = false;
let hungery = false;
let isMarried = true;
```
### 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 will be undefined.
```js
let firstName;
console.log(firstName); //not defined, because it is not assigned to a value yet
```
### Null
```js
let empty = null;
console.log(empty); // -> null , means no value
```
# Operators
## Assignment operators
An equal sign in JavaScript is an assignment operator. It uses to assign a variable.
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 Microsoft Academy 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 first 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(hint, use replace and regular express)
```js
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!?'
