LearnViz CompSci
Home / Learn / Web Development / Promises

Intermediate Topic 19 of 51 Web Development

Promises

Objects representing eventual completion of an async operation.

How it works

A Promise is pending, then fulfilled or rejected; .then/.catch chain results, Promise.all runs in parallel, and async/await is syntactic sugar over them.

Where it is used

Sequencing async steps.

Common pitfall

Forgetting to return a promise in a chain or to await in a loop.

Where it fits in the course

Promises is topic 19 of 51 in Web Development, rated Intermediate. It follows Asynchronous JavaScript. The next topic is Event Loop.

Practice and explore

How to study this topic

  1. Read the explanation above and restate the definition in your own words.
  2. Open the interactive lesson and answer its mini quiz.
  3. Read the common pitfall, then write a short example that avoids it.
  4. Check your understanding in the Web Development quiz, and revisit the topic if you miss a question.

Frequently asked questions

What is Promises?
Objects representing eventual completion of an async operation. It belongs to Web Development and is an intermediate-level topic.
Where do people use Promises?
Sequencing async steps.
What is the most common mistake with Promises?
Forgetting to return a promise in a chain or to await in a loop.
What should I learn before this topic?
Start with Asynchronous JavaScript, the topic just before it in Web Development.
How can I practice it?
Answer the mini quiz in the interactive lesson, then take the Web Development quiz.
Is Promises hard to learn?
It is an Intermediate topic. Be comfortable with the Beginner topics in this area first, then read the common pitfall carefully, since it is where most mistakes happen.
How long does it take to learn Promises?
Most learners can read the explanation and finish the interactive lesson in under an hour. Fluency comes from applying the idea, so plan a few short practice sessions with the quiz.
Which topics are related to Promises?
Asynchronous JavaScript, Event Loop, Browser DevTools are closely connected. The full list is in the related topics section of this page.
What should I study after Promises?
Continue with Event Loop, the next topic in Web Development.

Related topics