All the API’s of Node.js library are asynchronous means non-blocking. A Node.js based server never waits for an API to return data. The Node.js server moves to the next API after calling it, and a notification mechanism of Events of Node.js responds to the server for the previous API call.

In the context of Node.js, an asynchronous API is one that allows operations to be performed concurrently without blocking the execution of other code. This means that instead of waiting for a task to complete before moving on to the next one, the program can continue executing other tasks while waiting for certain operations (such as file I/O, network requests, or database queries) to finish.

Asynchronous APIs typically involve the use of callbacks, Promises, or async/await syntax in JavaScript to handle the results of asynchronous operations. These mechanisms enable developers to write non-blocking code that can handle multiple tasks simultaneously, improving the overall performance and responsiveness of Node.js applications.