safe-promises

Safe Promises in JavaScript

Promises go wrong too often.

• It's too easy to forget to catch a promise.
• Sometimes promises just stop in their tracks.

SafePromise doesn't let you forget, and makes sure to time out with an error.

Installation

Just run:

$ npm install --save safe-promises

Examples

By splitting the construction of the promise pipeline from the execution, we can ensure that we always pass in a final catch handler. It looks something like this:

let safePromises = require('safe-promises');
 
let SafePromise = safePromises.timeOutAfter(1000).failWith(console.error);
 
new SafePromise((resolve, reject) => resolve(5))
    .then((value) => {
        if (value % 2 == 1) {
            throw new Error('No odd numbers allowed.');
        }
        return value;
    })
    .perform();

That will fail, and even though we haven't provided an explicit catch for the promise, we've constructed it with a failure handler that logs to console.error, so we know we'll never have to worry about it.

If you need different sorts of error handlers, just construct different SafePromise classes. Here, we're setting a timeout of 5 seconds, after which the default timeout error will be passed to the error handler instead.

let UIPromise = safePromises.timeOutAfter(5000).failWith((error) => {
    $('#error').text(error.message).show();
});
 
UIPromise.resolve(user.name)
    .then(lookupUser)
    .perform();