In 1989, Tim Berners-Lee proposed the World Wide Web at CERN to help researchers share information. Documents could link to other documents, letting readers follow connections between information stored on different computers. What began as a way to share research grew into a platform for shopping, banking, work, entertainment, and just about everything else we have managed to squeeze into a browser!
The web runs over the internet through exchanges between clients and servers. Your browser is a client: it uses a URL to identify a resource and sends an HTTP request to a server, which sends a response back. For a web page, HTML describes the content and links, and JavaScript adds behavior by running code in your browser. The server can run code of its own to look up an account, save a message, or process a payment. Shared protocols and formats let the same browser interact with sites built by people who have never met.
All of this puts a lot of software, data, and authority within reach of a web request. Servers accept input from strangers, browsers execute code supplied by websites, and applications decide who gets access to private information. Those interactions have to remain safe even when someone deliberately sends the unexpected. Throughout this dojo, you'll look beneath the pages and buttons, follow the messages and code that make them work, and find out what happens when the assumptions behind them break.
