Pending state

As explained in Secrets of the JavaScript Ninja, Second Edition

The promise state in which the final outcome has not yet been determined.

A promise is pending while its asynchronous result is still unknown. This unresolved state lasts until the promise fulfills with a value or rejects with an error. section 6.3.2

A promise leaves the pending state in either of two ways:

• Calling resolve fulfills the promise with the promised value. section 6.3.2
• Calling reject, or encountering an unhandled exception during promise handling, rejects it. section 6.3.2
• Once fulfilled or rejected, a promise cannot switch to the other state. section 6.3.2

Waiting for a timeout

A promise that resolves after a 500-millisecond timeout remains pending while it waits. When the timeout calls resolve with “Hattori,” the promise fulfills. section 6.3.2

Figure 6.10. States of a promise

Use the state diagram to follow a promise from pending to either fulfilled or rejected. section 6.3.2

How Secrets of the JavaScript Ninja, Second Edition covers it

How deep it goes

Defines the state transitions to fulfillment or rejection and notes that settled promises cannot switch states.

Examples

Uses a 500-millisecond timeout to delay resolving a promise with “Hattori.”

What you can do after

Understand how pending differs from fulfilled and rejected promise states.

How it connects

Connects promise state to the resolve and reject functions and to the fulfilled and rejected states.

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Also explained in

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  liveBookmanning.com
  Acing the Certified Kubernetes Administrator Exam, Second EditionA pending state is a Kubernetes pod phase in which the pod has been accepted but is not yet running, commonly because it has not been scheduled.
• 

  liveBookmanning.com
  Rust Servers, Services, and AppsPoll::Pending is a Rust polling result indicating that an asynchronous computation is not yet ready to produce its output.

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Related concepts

• promisepart of · A JavaScript Promise is an object representing the eventual completion or failure of an asynchronous operation and its resulting value or reason.
• readycontrasts with · Poll::Ready is a Rust asynchronous computation result containing the computation's completed output.
• spinnerproduces · A spinner is an animated user-interface indicator that signals an ongoing, pending, or waiting operation without specifying its completion state.
• pending setused by · A pending set is the set returned by asyncio.wait containing awaitables that have not completed when the wait returns.

This explainer was generated by Manning's knowledge graph from the text of Secrets of the JavaScript Ninja, Second Edition. The section links point to the parts of the book it draws on.