API Reference > ecschema-metadata > Utils > DelayedPromise DelayedPromise<T> Class Beta 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?: | (reason: any) => TResult | PromiseLike<TResult>): Promise<T | TResult> Attaches a callback for only the rejection of the Promise. finally(onFinally?: | () => void): Promise<T> Attaches a callback for only the finally clause of the Promise. then<TResult1, TResult2>(onfulfilled?: | (value: T) => TResult1 | PromiseLike<TResult1>, onrejected?: | (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> [toStringTag] Readonly "Promise" Defined in core/ecschema-metadata/src/DelayedPromise.ts Line 30 Last Updated: 11 June, 2024