Abortable-promise-chain NPM

abortable-promise-chain

A Promise subclass to make the promise chain abortable.

Why?

Sometimes in a promise chain, you need to abort the chain and prevent any additional then/catch/finally from running.

In simple cases, this can be done by just throwing an exception and catching it at the end of the chain. But let's imagine a more complex chain: multiple different catch handlers, handling different kinds of exceptions, only some of which are fatal. As complexity grows it's harder and harder (also uglier and harder to read) to make this happen.

That's why I wrote this package.

Installation

To install the package, just run:

npm install abortable-promise-chain --save

Import it in your code and start using it:

import AbortablePromise from 'abortable-promise-chain';

AbortablePromise.from(someApiCall())
  .then((res, abort) => {
    if (res.isTheSkyBlue) {
      abort();
    }
    return res;
  })
  .then(res => {
    // this won't run.
  });

If you are using it in node, require it like this:

const AbortablePromise = require('abortable-promise-chain').default;

Usage

There are two ways of creating an AbortablePromise:

From an executor function, just like we would use for creating a normal Promise:

const executor = (resolve, reject) => setTimeout(() => resolve('data'), 1000);
const abortable = new AbortablePromise(executor);

From an already created normal Promise. (Note that we are using the from static method instead of the constructor here)

const promise = fetch('some url');
const abortable = AbortablePromise.from(promise);

Our AbortablePromise is working the same as a normal Promise, except for one thing.

Every handler we pass to the then / catch / finally methods is getting an extra, second parameter which is the abort function. This can be used to (surprise!) abort the chain. That means no additional then / catch / finally handlers will be called and the promise will never be resolved or rejected.

Note that finally normally doesn't get any parameters, but we still use the second parameter for the abort function (for consistency), so you need to ignore the first one (which is always undefined).

// ...continuing the previous example

abortable
  .then((res, abort) => {
    // i can call abort here,
  })
  .catch((err, abort) => {
    // or here,
  })
  .finally((_, abort) => {
    // or here.
  });

Unlike some alternatives, AbortablePromise allows you to abort the chain from the inside. And even if you return a normal Promise or a value from a handler, it gets automatically wrapped, so you don't loose the abort capability further down.

AbortablePromise.from(fetch('json url'))
  .then(res => res.json()) // that's a normal promise,
  .then((res, abort) => {
    // but i can still call abort here,
    if (res.isTheSeaWet) {
      abort();
    }
    return res;
  })
  .then(res => {
    // so this won't run.
  });

Supported browsers

The package is transpiled to ES5 with Babel, using the "defaults" browserlist. You can run npx browserslist "defaults" in your terminal to see the list of browsers.

Node.js is also supported.