**Can You Cancel the Chain in JavaScript Promises?**

Canceling a Vanilla ECMAScript 6 Promise Chain

Problem

Is it possible to clear the event handlers .thens for a JavaScript Promise instance?

Background

When a test using a particular framework times out, the timeout Promise calls assert.fail() to mark the test as failed. However, the test continues to run because the test Promise (result) is still waiting to resolve.

Desired Solution

Ideally, the remaining .thens on the result variable could be cleared to prevent further execution of the test.

Answer

Unfortunately, there is no built-in method in ECMAScript 6 to cancel Promises or their .thens handlers. The ES committee is still discussing potential solutions that may be adopted in future ECMAScript versions.

Possible Workarounds

Until an official solution is implemented, you can consider the following workarounds:

• Subclassing: Create your own subclass of Promise that incorporates cancellation logic.
• Userland Promise Implementations: Explore third-party Promise implementations that provide cancellation functionality, such as cancelable-promise or promise-cancellation.

Additional Notes

In the specific case mentioned in the problem, the issue with the test not ending was due to an uncaught error in the test function. To resolve this, you should handle errors appropriately within the test function.

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