API Reference

LazyPromise<T> is a generic class that is the default export.

Constructor

constructor(executor: LazyPromise<T>["executor"])

• executor: (resolve: (value: T) => void, reject: (reason?: any) => void) => void

Creating an instance does not immediately execute the executor.

Instance properties

executor

Type: (resolve: (value: T) => void, reject: (reason?: any) => void) => void

The executor function passed to the constructor.

promise

Type: Promise<T> | null

The internal native Promise. Its value is null when not initialized; it becomes non-null after then / catch / finally is triggered for the first time.

Instance methods

then(onfulfilled?, onrejected?)

Initializes the internal Promise and returns Promise<T>.

lazy.then(
  (value) => { /* handle fulfilled */ },
  (reason) => { /* handle rejected */ }
);

catch(onrejected?)

Initializes the internal Promise and returns Promise<T>.

lazy.catch((reason) => { /* handle rejected */ });

finally(onfinally?)

Initializes the internal Promise and returns Promise<T>.

lazy.finally(() => { /* cleanup */ });

initPromise()

Internal method: initializes with new Promise<T>(this.executor) when this.promise is null. It is invoked only inside then / catch / finally and usually does not need to be used manually.

Note: initPromise is declared as a public method, but semantically it is an internal implementation. For actual use, please refer to then / catch / finally.

Return type notes

The declared return types of then / catch / finally are Promise<T> (see dist/index.d.ts). In the source, the internal Promise is guaranteed to be initialized via this.initPromise(), and then the result is returned using this.promise?.then(...).

Implementation behavior notes

• The executor is executed only once (when initPromise is triggered for the first time).
• If continued on the Promise chain, the return value follows the native Promise behavior.

References

• Overview
• Quick Start