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Advanced Topic 40 of 51 Web Development

CORS

Browser policy controlling cross-origin requests.

How it works

The browser's same-origin policy blocks cross-origin reads; servers opt in with Access-Control-Allow-Origin headers, and preflight OPTIONS requests check non-simple requests.

Where it is used

Front-end on one domain calling an API on another.

Common pitfall

Using * with credentials is disallowed; CORS is enforced by browsers, not servers.

Where it fits in the course

CORS is topic 40 of 51 in Web Development, rated Advanced. It follows OAuth 2.0. The next topic is Web Security Basics.

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 CORS?
Browser policy controlling cross-origin requests. It belongs to Web Development and is an advanced-level topic.
Where do people use CORS?
Front-end on one domain calling an API on another.
What is the most common mistake with CORS?
Using * with credentials is disallowed; CORS is enforced by browsers, not servers.
What should I learn before this topic?
Start with OAuth 2.0, 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 CORS hard to learn?
It is an Advanced topic. Expect to read the explanation more than once and to connect it with earlier topics. Working through a small example by hand helps most.
How long does it take to learn CORS?
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 CORS?
OAuth 2.0, Web Security Basics, JWT are closely connected. The full list is in the related topics section of this page.
What should I study after CORS?
Continue with Web Security Basics, the next topic in Web Development.

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