Asynchronous I/O Lesson

### Concept Window Asynchronous I/O lets a program start a task that may take time without freezing everything else. Loading a file, calling an API, or waiting for a database response should not stop the whole page from working. Promises represent values that will be available later. The async and await keywords make promise-based code easier to read because it looks closer to normal step-by-step code.

Code Runner Challenge

Asynchronous I/O Lesson

View IPYNB Source 
%%js

// CODE_RUNNER: Asynchronous I/O Lesson

async function loadMessage() {
  console.log("Request started");

  const response = await fetch("/message.txt");
  const text = await response.text();

  console.log("Message loaded: " + text);
}

loadMessage();
console.log("This can run while the request is waiting");
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Output
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The request starts inside the async function, but the rest of the program can continue. When the response arrives, await gives the function the loaded text.