Catching errors with catch

Learn to catch a promise rejection and use the error message.

Catching errors with catch

When a promise rejects, you catch the error with the catch method. catch sits at the end of the chain and receives the rejection reason.

loadOrder()
  .then(order => console.log(order))
  .catch(error => console.log(error));

A rejection flows down the chain; each then is skipped until a catch handles it. This lets you handle errors in one place and avoid repeated checks from callbacks.

catch enables recovery

catch is shorthand for then(null, onRejected); it handles only the failure case. After you catch an error, the value you return from catch creates a new fulfilled promise and the chain continues normally.

loadOrder()
  .catch(error => 'default')
  .then(order => console.log(order));

This lets you recover from an error and continue the chain. You can show fallback data to the user this way.

Exercise Build a then and catch chain

A function called fetchPrice returns a promise. Call fetchPrice; in then log the price with console.log; add catch at the end of the chain and log the error with console.log.

Show example solution

fetchPrice()
  .then(price => console.log(price))
  .catch(error => console.log(error));

Test yourself

What parameter does catch take?
- The resolved value
- The promise object
- An array
- The rejection reason
Show answer

The rejection reason — Correct! catch receives the rejection reason.

Add catch to the chain

loadOrder()
  .then(order => console.log(order))
  .____(error => console.log(error));

Show answer

loadOrder()
  .then(order => console.log(order))
  .catch(error => console.log(error));

Match catch concepts

catch

Catches a rejection
then(null, fn)

Same job as catch
value from catch

Creates a new fulfilled promise

Next lesson: Cleanup with finally

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