Wrap handlers

[yoshuawuyts]

Adds the functionality described in choojs/choo#145. Builds on #58. Pretttttty excited about this ✨

• implementation
• docs
• tests

[coveralls]

Coverage increased (+0.5%) to 95.152% when pulling 7e17e82 on wrap-handlers into b381a97 on master.

[myobie]

I am very excited about this. I already created an effectWrapper function that returns a wrapped function so I can use another promise based storage api more easily in the effects, but I have to use it repeatedly in my model.

An example I have is:

export function wrapEffect (cb) {
  return async (data, state, send, done) => {
    const newSend = (action, data = null) => {
      return new Promise((resolve, reject) => {
        send(name, data, (err, res) => {
          if (err) {
            done(err) // communicate error to choo
            reject(err) // throw
          } else {
            resolve(res) // move forward
          }
        })
      })
    }
    await cb(data, state, newSend)
    done() // auto-done when everything is done
  }
}

which allowed me to write this in the end:

app.model({
  effects: {
    reloadMailsCount: wrapEffect(async (data, state, send) => {
      const count = await storage.getMailsCount()
      await send('receiveMailsCount', count)
    })
  }
})

Is this the type of thing you are hoping to enable?

[yoshuawuyts]

@myobie Hah yeah, pretty much! I'm a strong opponent of Promises myself, but I want people that like them to be able to use them as they please (as with other paradigms).

A little note: for your implementation to be correct you'd probably have to wrap it in a try ... catch so any errors that bubble up can be caught for the send(err) call. Also probably cool to allow it to return a value synchronously which would be passed into send(null, value) ✨

[myobie]

@yoshuawuyts great idea, I will do that. And yes, promises + try/catch do sometimes make my head hurt.

I'm not entirely sure what send(null, value) would do, so I will do some research there.

[yoshuawuyts]

@myobie so when calling send(name, data, callback(err, res)) the receiving method can trigger the callback by calling done(err, res). It's basically delegation of control, and once it's done it either returns an error or data (where data can be null / undefined). This essentially creates a CSP style system. This is not explicitly mentioned anywhere though (yay for docs) but figured I'd mention it here so that you can at least have a good time implementing a package in this fashion (':

[coveralls]

Coverage decreased (-0.5%) to 97.972% when pulling e6c28e0 on wrap-handlers into 7756160 on master.

[coveralls]

Coverage increased (+0.2%) to 98.586% when pulling e72f758 on wrap-handlers into 7756160 on master.