**Congratulations** for deciding to participate in 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 concept of programming. In the end of the challenge you will get a 30DaysOfJavaScript programming challenge completion certificate. In case you need help or if you would like to help others you may 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 too. JavaScript is the language of the web.
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
I believe you have the motivation and a strong desire to be a developer, computer and Internet. If you have those, then you have everything to get started.
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.
You can open Google Chrome console either by clicking three dots at the top right corner of the browser, selecting _More tools -> Developer tools_ or using a keyboard shortcut. I prefer using shortcuts.
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 changes your JavaScript code to machine code.
Let us write a JavaScript code on the Google Chrome console:
We can write any JavaScript code on the Google console or any browser console. However, for this challenge, we only focus on Google Chrome console. Open the console using:
To write our first JavaScript code, we used a built-in function **console.log()**. We passed an argument as input data, and the function displays the output. We passed 'Hello, World' as input data or argument in the console.log() function.
We add comments to our code. Comments are very important to make code more readable and to leave remarks in our code. JavaScript does not execute the comment part of our code. Any text line starting with // in JavaScript is a comment or anything enclosed like this /* */ is a comment.
Programming languages are similar to human languages. English language or any other language uses words, phrases, sentences,compound sentences and other more to convey a meaningful message. The English meaning of syntax is *the arrangement of words and phrases to create well-formed sentences in a language*. The technical definition of syntax is *the structure of statements in a computer language.* Programing languages have syntax. JavaScript is a programming language and like other programming languages it has its own syntax. If we do not write a syntax that JavaScript understands, it will raise different types of errors. We will explore different kinds of JavaScript errors later. For now, let us see syntax errors.
I made a deliberate mistake. As a result, the console raises a syntax error. Actually, the syntax is very informative. It informs what type of mistake we made. By reading the error feedback guideline, we can correct the syntax and fix the problem. 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 the single quote, double quote, or a backtick quote.
We can write our codes on the browser console, but it won't do for bigger projects. In a real working environment, developers use different code editors to write their codes. In this 30 days JavaScript challenge, we will use Visual Studio Code.
Visual studio code is a very popular open-source text editor. I would recommend to [download Visual Studio Code](https://code.visualstudio.com/), but if you are in favor of other editors, feel free to follow with what you have.
Open the Visual Studio Code by double-clicking its icon. When you open it, you will get this kind of interface. Try to interact with the labeled icons.
Create a folder on your desktop and call it 30DaysOfJS or in any location and create an **_index.html_** file in the project folder. Then paste the following code and open it in a browser, for example [Chrome](https://www.google.com/chrome/).
This is how we write an internal script most of the time. Writing the JavaScript code in the body section is the most preferred option. Open the browser console to see the output from the console.log()
First, we should create an external JavaScript file with .js extension. All files ending with .js extension are JavaScript files. 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_.
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.
Variables are _containers_ of data. Variables used to _store_ data in a memory location. When a variable is declared, a memory location is reserved. When a variable is assigned to a value (data), the memory space will be filled with that data. To declare a variable, we use _var_, _let_, or _const_ keywords. We will talk more about var, let, and const in detail in other sections (scope). For now, the above explanation is enough.
For a variable that changes at a different time, we use _let_. If the data does not change at all, we use _const_. For example, PI, country name, gravity do no change, and we can use *const*. We will not use var in this challenge and I don't recommend you to use it. It is error prone way of declaring variable it has lots of leak.
Let us declare variables with different data types. To declare a variable, we need to use let or const keyword before the variable name. Following the variable name, we write an equal sign (assignment operator), and a value.
🌕 You are amazing! You have just completed day 1 challenge and you are on your way to greatness. Now do some exercises for your brain and for your muscle.
