Can JavaScript connect with MySQL?

If you want to connect to a MySQL database using JavaScript, you can use Node.js and a library called mysql. You can create queries, and get results as an array of registers. If you want to try it, you can use my project generator to create a backend and choose MySQL as the database to connect. Then, just expose your new REST API or GraphQL endpoint to your front and start working with your MySQL database.

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OLD ANSWER LEFT BY NOSTALGIA

THEN

As I understand the question and correct me if I am wrong, it refers to the classic server model with JavaScript only on the client-side. In this classic model, with LAMP servers (Linux, Apache, MySQL, PHP) the language in contact with the database was PHP, so to request data to the database you need to write PHP scripts and echo the returning data to the client. Basically, the distribution of the languages according to physical machines was:

1. Server Side: PHP and MySQL.
2. Client Side: HTML/CSS and JavaScript.

This answered to an MVC model (Model, View, Controller) where we had the following functionality:

1. MODEL: The model is what deals with the data, in this case, the PHP scripts that manage variables or that access data stored, in this case in our MySQL database and send it as JSON data to the client.
2. VIEW: The view is what we see and it should be completely independent of the model. It just needs to show the data contained in the model, but it shouldn't have relevant data on it. In this case, the view uses HTML and CSS. HTML to create the basic structure of the view, and CSS to give the shape to this basic structure.
3. CONTROLLER: The controller is the interface between our model and our view. In this case, the language used is JavaScript and it takes the data the model send us as a JSON package and put it inside the containers that offer the HTML structure. The way the controller interacts with the model is by using AJAX. We use GET and POST methods to call PHP scripts on the server-side and to catch the returned data from the server.

For the controller, we have really interesting tools like jQuery, as "low-level" library to control the HTML structure (DOM), and then new, more high-level ones as Knockout.js that allow us to create observers that connect different DOM elements updating them when events occur. There is also Angular.js by Google that works in a similar way, but seems to be a complete environment. To help you to choose among them, here you have two excellent analyses of the two tools: Knockout vs. Angular.js and Knockout.js vs. Angular.js. I am still reading. Hope they help you.

NOW

In modern servers based in Node.js, we use JavaScript for everything. Node.js is a JavaScript environment with many libraries that work with Google V8, Chrome JavaScript engine. The way we work with these new servers is:

1. Node.js and Express: The mainframe where the server is built. We can create a server with a few lines of code or even use libraries like Express to make even easier to create the server. With Node.js and Express, we will manage the petitions to the server from the clients and will answer them with the appropriate pages.
2. Jade: To create the pages we use a templating language, in this case, Jade, that allow us to write web pages as we were writing HTML but with differences (it take a little time but is easy to learn). Then, in the code of the server to answer the client's petitions, we just need to render the Jade code into a "real" HTML code.
3. Stylus: Similar to Jade but for CSS. In this case, we use a middleware function to convert the stylus file into a real CSS file for our page.

Then we have a lot of packages we can install using the NPM (Node.js package manager) and use them directly in our Node.js server just requiring it (for those of you that want to learn Node.js, try this beginner tutorial for an overview). And among these packages, you have some of them to access databases. Using this you can use JavaScript on the server-side to access My SQL databases.

But the best you can do if you are going to work with Node.js is to use the new NoSQL databases like MongoDB, based on JSON files. Instead of storing tables like MySQL, it stores the data in JSON structures, so you can put different data inside each structure like long numeric vectors instead of creating huge tables for the size of the biggest one.

I hope this brief explanation becomes useful to you, and if you want to learn more about this, here you have some resources you can use:

• Egghead: This site is full of great short tutorials about JavaScript and its environment. It worths a try. And the make discounts from time to time.
• Code School: With a free and very interesting course about Chrome Developer tools to help you to test the client-side.
• Codecademy: With free courses about HTML, CSS, JavaScript, jQuery, and PHP that you can follow with online examples.
• 10gen Education: With everything you need to know about MongoDB in tutorials for different languages.
• W3Schools: This one has tutorials about all this and you can use it as a reference place because it has a lot of shortcode examples really useful.
• Udacity: A place with free video courses about different subjects with a few interesting ones about web development and my preferred, an amazing WebGL course for 3D graphics with JavaScript.

I hope it helps you to start.

Have fun!

Client-side JavaScript cannot access MySQL without some kind of bridge. But the above bold statements that JavaScript is just a client-side language are incorrect -- JavaScript can run client-side and server-side, as with Node.js.

Node.js can access MySQL through something like https://github.com/sidorares/node-mysql2

You might also develop something using Socket.IO

Did you mean to ask whether a client-side JS app can access MySQL? I am not sure if such libraries exist, but they are possible.

EDIT: Since writing, we now have MySQL Cluster:

The MySQL Cluster JavaScript Driver for Node.js is just what it sounds like it is – it’s a connector that can be called directly from your JavaScript code to read and write your data. As it accesses the data nodes directly, there is no extra latency from passing through a MySQL Server and need to convert from JavaScript code//objects into SQL operations. If for some reason, you’d prefer it to pass through a MySQL Server (for example if you’re storing tables in InnoDB) then that can be configured.

• JSDB offers a JS interface to DBs.

• A curated set of DB packages for Node.js from sindresorhus.