API Reference › ecschema-metadata› Utils › DelayedPromise

DelayedPromise<T> Class

Similar to a normal Promise, a DelayedPromise represents the eventual completion (or failure) and resulting value of an asynchronous operation that has not yet started.

The asynchronous operation behind a DelayedPromise will start when any of the following occurs:

  • The DelayedPromise is awaited.
  • A callback is attached via .then() or .catch(() => { }).
  • The asynchronous operation is explicitly started via .start()

Just as normal Promises will never return to their pending state once fulfilled or rejected, a DelayedPromise will never re-execute its asynchronous operation more than once.

Ultimately, a DelayedPromise is nothing more than some syntactic sugar that allows you to represent an (asynchronously) lazily-loaded value as an instance property instead of a method. You could also accomplish something similar by defining an async function as a property getter. However, since a property defined as a DelayedPromise will not start simply by being accessed, additional (non-lazily-loaded) "nested" properties can be added.

Remember: Unlike regular Promises in JavaScript, DelayedPromises represent processes that may not already be happening.

Implements

  • Promise<T>

Methods

Name Description
constructor<T>(startCallback: () => Promise<T>): DelayedPromise<T> Constructs a DelayedPromise object.  
catch<TResult>(onrejected?: "null" | (reason: any) => TResult | PromiseLike<TResult>): Promise<T | TResult> Attaches a callback for only the rejection of the Promise.  
finally(onFinally?: "null" | () => void): Promise<T> Attaches a callback for only the finally clause of the Promise.  
then<TResult1, TResult2>(onfulfilled?: "null" | (value: T) => TResult1 | PromiseLike<TResult1>, onrejected?: "null" | (reason: any) => TResult2 | PromiseLike<TResult2>): Promise<TResult1 | TResult2> Attaches callbacks for the resolution and/or rejection of the Promise.  

Properties

Name Type Description
start () => Promise<T> Explicitly starts the asynchronous operation behind this DelayedPromise (if it hasn't started already).  
[toStringTag] Readonly "Promise"    

Defined in

Last Updated: 21 November, 2024