Callback Error Model

callback.js

'use strict';

const mockClient = {};

// The Callback Error Model allows unintentional errors to bubble up and crash
// the process.
//
// With the Callback Error Model, it is impossible to catch these errors
// because try/catch doesn't work over subsequent ticks of the event loop.
//
// Errors that can be handled are propagated via callbacks.

function doStuff(cb) {
    let rand = Math.random();
    let x;

    if (rand > 0.7) {
        // throws a TypeError
        // imagine this leaks a socket underneath the hood.
        // $ echo $? => 1
        mockClient.call();
    } else if (rand > 0.3) {
        // return error to be handled
        // $ echo $? => 0
        return cb(new Error('handle me!'))
    }
    // happy path
    // $ echo $? => 0
    return cb(null, 'success');
}

doStuff(function(err, msg) {
    if (err) {
        console.error('completed with non-fatal err: ', err);
    } else {
        console.log('completed!', msg);
    }
});