golike-defer

golike-defer

go's defer statement in JavaScript

defer() is a function decorator which injects a $defer() function as a first parameter.

This injected function can be used to register deferreds, functions which will be executed at the end of the decorated function execution, no matter how it ended (via a return or a throw).

Note: the deferreds are executed in the reverse order of their declarations.

Install

Installation of the npm package:

> npm install --save golike-defer

Usage

• $defer(cb): cb will be called at the end of the function
• $defer(cb, arg1, arg2): cb will be called with arg1 and arg2 arguments
• $defer.call(thisArg, cb): cb will be called with the context thisArg
• $defer.call(thisArg, 'method'): thisArg.method will be called at the end of the function

import defer from 'golike-defer'
import fs from 'fs'

const readFileSync = defer(($defer, path) => {
  const fd = fs.openSync(path, 'r')

  // The file will be automatically closed at the end of the function,
  // whether it succeed or failed.
  $defer(fs.closeSync, fd)

  const { size } = fs.statSync(path)

  const buffer = Buffer.allocUnsafe(size)
  fs.readSync(fd, buffer, 0, buffer.length)

  return buffer
})

// Helper to promisify a function call.
const fromCallback = fn => new Promise((resolve, reject) => {
  fn((error, result) => error ? reject(error) : resolve(result))
})

const readFile = defer(async ($defer, path) => {
  const fd = await fromCallback(cb => fs.open(path, 'r', cb))

  // The file will be automatically closed at the end of the function,
  // whether it succeed or failed.
  $defer(() => fromCallback(cb => fs.close(fd, cb)))

  const { size } = await fromCallback(cb => fs.stat(path, cb))

  const buffer = Buffer.allocUnsafe((size)
  await fromCallback(cb => fs.read(fd, buffer, 0, buffer.length, cb))

  return buffer
})

There are also two decorators, defer.onSuccess() and defer.onFailure() which run the deferreds only, respectively, in case of success or in case of failure.

On error

Exceptions (or rejected promises) thrown in deferred are caught and printed on the console.

This can be customized with the onError() method:

const myDefer = defer.onError(error => {
  log(error)
})

const fn = myDefer(($defer, arg1, arg2) => {
  // ...
})

Development

# Install dependencies
> npm install

# Run the tests
> npm test

# Continuously compile
> npm run dev

# Continuously run the tests
> npm run dev-test

# Build for production (automatically called by npm install)
> npm run build

Contributions

Contributions are very welcomed, either on the documentation or on the code.

You may:

• report any issue you've encountered;
• fork and create a pull request.

License

ISC © Julien Fontanet