@kawaz/provide-defer NPM

@kawaz/provide-defer

@kawaz/provide-defer is a TypeScript utility package that provides a mechanism for deferring the execution of functions or Promises, similar to Go's defer statement. It allows you to schedule cleanup or finalization code to run after the main function has completed, regardless of whether it completes normally or throws an error.

Features

Defer execution of functions or Promises
Execute deferred functions in reverse order (LIFO)
Options for error handling and asynchronous execution
Aggregates errors from main and deferred functions
TypeScript support with generic typing

Installation

npm install @kawaz/provide-defer

Usage

Here's a basic example of how to use provideDefer:

import { provideDefer } from '@kawaz/provide-defer';

const result = await provideDefer(async (defer) => {
  const resource = await acquireResource();
  defer(() => releaseResource(resource));

  // Use the resource...
  return someOperation(resource);
});

API

`provideDefer<T>(fn: (defer: DeferFunction) => T | Promise<T>): Promise<T>`

fn: The main function to execute. It receives a defer function as an argument.
Returns a Promise that resolves with the result of the main function.

`DeferFunction`

type DeferFunction = (fn: FunctionOrPromise<unknown>, options?: DeferOptions) => void

fn: The function or Promise to be deferred.
options: Optional settings to control the behavior of the deferred function.

`DeferOptions`

type DeferOptions = {
  noThrow?: boolean;
  noWait?: boolean;
}

noThrow: If true, errors from this deferred function will be ignored.
noWait: If true, the execution of the deferred function will start as scheduled, but provideDefer will not wait for its completion before resolving. This allows the deferred function to run in the background.

Error Handling

If any errors occur in the deferred functions (and noThrow is not set), or if the main function throws an error, provideDefer will throw an AggregateError containing all the errors.

Examples

Basic Usage

import { provideDefer } from '@kawaz/provide-defer';

const result = await provideDefer((defer) => {
  defer(() => console.log('This will be executed last'));
  defer(() => console.log('This will be executed second'));
  console.log('This will be executed first');
  return 'Main function result';
});

console.log(result);
// Outputs:
// This will be executed first
// This will be executed second
// This will be executed last
// Main function result

Error Handling

import { provideDefer } from '@kawaz/provide-defer';

try {
  await provideDefer((defer) => {
    defer(() => { throw new Error('Deferred error 1'); });
    defer(() => { throw new Error('Deferred error 2'); });
    throw new Error('Primary error');
  });
} catch (error) {
  if (error instanceof AggregateError) {
    console.log(error.message); // Outputs: 'Main error: "Primary error". Additionally, 2 deferred error(s) occurred.'
    console.log(error.errors);
    // Array of all errors: The main error is the first element, followed by deferred errors
    // [
    //   Error: Primary error,
    //   Error: Deferred error 2,
    //   Error: Deferred error 1
    // ]
  }
}

Using `noThrow` and `noWait` Options

import { provideDefer } from '@kawaz/provide-defer';

await provideDefer((defer) => {
  defer(() => { throw new Error('This error will be ignored'); }, { noThrow: true });

  defer(async () => {
    console.log('Start of long-running operation');
    await new Promise(resolve => setTimeout(resolve, 5000));
    console.log('End of long-running operation');
  }, { noWait: true });

  console.log('Main function continues immediately');
  return 'Main function result';
});

console.log('provideDefer resolved');

// Output:
// Start of long-running operation
// Main function continues immediately
// provideDefer resolved
// End of long-running operation (after about 5 seconds)