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JavaScript is easy when all you need is a simple working interface. Responsiveness is usually achieved through the use of asynchronous functions. This means that you can let your code do several things at the same time without stopping or blocking the main thread. JavaScript provides a concurrency model based on an event loop, which executes the code, collecting and processing events, and performs queued sub-tasks. The browser will still drop the function into the web API, and the program will continue to work. You can use callback, promises or await with understanding how it works in the browser.