Node.js template to support promise/async/await

[padiazg]

Signed-off-by: Patricio Diaz [email protected]

This template introduces the possibility of using Promise or Async/Await on the handler function, in addition of the callback approach used before.

Description

In index.js the value returned by handler.js is checked to figure out if it is the final result or is a Promise so it can be retrieved and handled properly.

Motivation and Context

We need to handle the latest asynchronicity mechanism provided by the language, which are Promises and Async/Await

Fixes issue #92

• I have raised an issue to propose this change (required)

Which issue(s) this PR fixes

Fixes #92

How Has This Been Tested?

For a Callback version of handler.js

$ faas new node-cb --lang node --prefix padiazg

handler.js

"use strict"

// A simple delay function
const delayCallback = cb => {
    const min = 0; // 0 sec
    const max = 2; // 2 sec
    const delay = Math.round((Math.random() * (max - min) + min));
    setTimeout(() => cb(delay),  delay * 1000);
}

// callback version
module.exports = (context, callback) => {
    delayCallback(delay => callback(undefined, {status: context || "callback", delay}))
}

$ faas up -f node-cb.yml
$ echo -n "cb" | faas invoke node-cb -
{"status":"cb","delay":1}

For a Promise version of handler.js

$ faas new node-promise --lang node --prefix padiazg

handler.js

"use strict"

// A simple delay function
const delayCallback = cb => {
    const min = 0; // 0 sec
    const max = 2; // 2 sec
    const delay = Math.round((Math.random() * (max - min) + min));
    setTimeout(() => cb(delay),  delay * 1000);
}

// Uncomment the following line to use it with the promise or async/await versions
const delayPromise = () => new Promise(resolve => delayCallback(delay => resolve(delay)) )

module.exports = context => new Promise((resolve, reject) => {
    delayPromise()
    .then(delay => {
        resolve({status: context || "promise", delay});
    })
})

$ faas up -f node-promise.yml
$ echo -n "prom" | faas invoke node-promise -
{"status":"prom","delay":2}

For a Async/Await version of handler.js

$ faas new node-async-await --lang node --prefix padiazg

handler.js

"use strict"

// A simple delay function
const delayCallback = cb => {
    const min = 0; // 0 sec
    const max = 2; // 2 sec
    const delay = Math.round((Math.random() * (max - min) + min));
    setTimeout(() => cb(delay),  delay * 1000);
}

// Uncomment the following line to use it with the promise or async/await versions
const delayPromise = () => new Promise(resolve => delayCallback(delay => resolve(delay)) )

module.exports = async context => {
    const delay = await delayPromise();
    return {status: context || "async/await", delay}
}

$ faas up -f node-promise.yml
$ echo -n "async" | faas invoke node-async-await -
{"status":"async","delay":0}

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• [*] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Version change (see: Impact to existing users)

Impact to existing users

Hopefully wont break existing functions

Checklist:

• [*] My code follows the code style of this project.
• [*] My change requires a change to the documentation.
• I have updated the documentation accordingly.
• [*] I've read the CONTRIBUTION guide
• [*] I have signed-off my commits with git commit -s
• I have added tests to cover my changes.
• All new and existing tests passed.

[alexellis]

What is this for?

[padiazg]

The code in handler.js usually is an example that shows what the functions is meant to do. That delay function just simulates some delayed payload, to demonstrate how the async/await or promise works. It's just an example, like if we do an API call, or access a database, but without all the requirements for that.

[alexellis]

Will it still work if you reset this back to how it was?

All of the templates in the project are completely minimal example and this might be confusing for people that are used to the template already.

[padiazg]

Yes, it will work as usual. Then a suitable example will be just on the documentation?

[padiazg]

I'll leave it as the original, just adding the promises/async/await support for this template.

[padiazg]

Tell me, we will still support callback as a way to call handler.js?

[alexellis]

I've tested these two combinations:

"use strict"

module.exports = (context, callback) => {
  callback(null, "done, via CB");
}

"use strict"

module.exports = async (context, callback) => {
  return "done";
}

Both worked as expected 👍

[alexellis]

LGTM