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defer ​

Create a promise with externally accessible resolve and reject methods.

Signature ​

typescript
function defer<T = void>(): {
  promise: Promise<T>;
  resolve: (value: T | PromiseLike<T>) => void;
  reject: (reason?: unknown) => void;
};

Returns ​

Object containing:

  • promise – The promise instance
  • resolve – Function to resolve the promise
  • reject – Function to reject the promise

Examples ​

Basic Usage ​

typescript
import { defer } from '@vielzeug/toolkit';
const deferred = defer<string>();
setTimeout(() => {
  deferred.resolve('Done!');
}, 1000);
const result = await deferred.promise;
console.log(result); // 'Done!'

Event-Based Workflow ​

typescript
import { defer } from '@vielzeug/toolkit';
const eventPromise = defer<Event>();
element.addEventListener(
  'click',
  (e) => {
    eventPromise.resolve(e);
  },
  { once: true },
);
const clickEvent = await eventPromise.promise;
console.log('Clicked at:', clickEvent.clientX, clickEvent.clientY);

Manual Control with Error Handling ​

typescript
import { defer } from '@vielzeug/toolkit';
const deferred = defer<number>();
if (someCondition) {
  deferred.resolve(42);
} else {
  deferred.reject(new Error('Condition not met'));
}
try {
  const value = await deferred.promise;
  console.log('Success:', value);
} catch (error) {
  console.error('Failed:', error);
}

Multiple Subscribers ​

typescript
import { defer } from '@vielzeug/toolkit';
const deferred = defer<string>();
// Multiple places can wait for the same promise
const promise1 = deferred.promise.then((result) => console.log('Handler 1:', result));
const promise2 = deferred.promise.then((result) => console.log('Handler 2:', result));
// Resolve once, both handlers execute
deferred.resolve('Shared result');
await Promise.all([promise1, promise2]);
  • race – Race promises with minimum delay
  • waitFor – Poll for a condition to become true