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Chapter XVII · Promises

Promise Chaining

Promise chaining allows sequential asynchronous operations to be linked together using `.then()` method returns.

01 How It Works

Think of an assembly line conveyor belt where each station processes data and passes it down to the next.

Every `.then()` handler returns a brand new settled promise, enabling clean sequential pipeline flows.

example.js
Promise.resolve(10)
  .then(val => val * 2)
  .then(result => console.log(result)); // 20

  1. 1. Call initial asynchronous promise.

  2. 2. Attach `.then()` handler transforming data.

  3. 3. Chain subsequent `.then()` or `.catch()` handlers seamlessly.

02 Practical Example

Here is how you might see this concept applied in real-world code:

practical.js
fetch("https://api.example.com/user")
  .then(res => res.json())
  .then(user => console.log(user.name))
  .catch(err => console.error(err));

Key Takeaway

Promise chaining eliminates callback hell, providing clean readable asynchronous workflows.

Related Concepts