How do you handle unhandled exceptions in asynchronous callbacks with Bluebird promises?

Asynchronous Exception Handling with Bluebird Promises

Q: How to handle unhandled exceptions in asynchronous callbacks with Bluebird promises?

Bluebird promises do not inherently catch exceptions thrown from asynchronous callbacks, unlike domains.

A: Use Promise Constructors or then() Closures to Handle Exceptions

To catch exceptions in async callbacks, wrap the callback in a promise constructor or then() closure:

<code class="javascript">function getPromise(){
    return new Promise(function(done, reject){
        setTimeout(function(){
            throw new Error("AJAJAJA");
        }, 500);
    }).then(function() {
        console.log("hihihihi");
        throw new Error("Oh no!");
    });
}</code>

Avoid Throwing in Custom Async Callbacks

Never throw exceptions directly in custom async callbacks (outside of promise callbacks). Instead, reject the surrounding promise:

<code class="javascript">function getPromise(){
    return new Promise(function(done, reject){
        setTimeout(done, 500);
    }).then(function() {
        console.log("hihihihi");
        reject(new Error("Oh no!"));
    });
}</code>

Example

Using a promise constructor:

<code class="javascript">var p = getPromise();
    p.then(function(){
        console.log("Yay");
    }).error(function(e){
        console.log("Rejected",e);
    }).catch(Error, function(e){
        console.log("Error",e);
    }).catch(function(e){
        console.log("Unknown", e);
    });</code>

Output:

Error [Error: Oh no!]

This approach ensures that exceptions are caught and handled appropriately, preventing the application from crashing.

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