Labels

When using the visual inspector, we would like to be able to distinguish tasks from each other, as well as seeing metadata about the tasks. We can do this by applying labels.

Labels are key/value pairs, the key must be a string and the value must be a string, number or boolean.

Labels also improve the "Effection trace" shown when an error occurs if you are using main, so even if you aren't using the visual inspector, adding some labels can make Effection code easier to debug.

We can apply labels when spawning a task:

import { run } from 'effection';

run(fetchWeekDay('cet'), {
  labels: {
    name: 'fetchWeekDay',
    timezone: 'cet'
  }
});

Or using spawn:

import { main, spawn } from 'effection';

main(function*() {
  yield spawn(fetchWeekDay('cet'), {
    labels: {
      name: 'fetchWeekDay',
      timezone: 'cet'
    }
  });
});

Or we can set labels on an operation by using the withLabels function:

import { main, withLabels } from 'effection';

main(function*() {
  yield withLabels(fetchWeekDay('cet'), {
    name: 'fetchWeekDay',
    timezone: 'cet'
  });
});

We could rewrite our fetchWeekDay operation to do this automatically for us:

import { fetch, withLabels } from 'effection';

export function fetchWeekDay(timezone) {
  return withLabels(function*() {
    let response = yield fetch(`http://worldclockapi.com/api/json/${timezone}/now`);
    let time = yield response.json();
    return time.dayOfTheWeek;
  }, { name: 'fetchWeekDay', timezone });
}

This way, wherever we use fetchWeekDay it would be nicely labeled and easily identifiable in the visual inspector.

Dynamic labels

Another way of setting labels is through the label operation. This operation makes it possible to set labels while the task is running:

import { once, label } from 'effection';

function *runSocketServer() {
  let socket = new WebSocket('ws://localhost:1234');

  yield label({ state: 'pending' });

  yield once(socket, 'open');

  yield label({ state: 'open' });

  console.log('socket is open!');

  let closeEvent = yield once(socket, 'close');

  yield label({ state: 'closed' });
  console.log('socket closed with code', closeEvent.code);
};

This can give you some insight into the current state of a task.

Function names

A final trick is that if our operation is a generator function, then we can name the function to automatically set the name label:

import { fetch, withLabels } from 'effection';

export function fetchWeekDay(timezone) {
  return function* fetchWeekDay() {
    let response = yield fetch(`http://worldclockapi.com/api/json/${timezone}/now`);
    let time = yield response.json();
    return time.dayOfTheWeek;
  }
}

Unfortunately, there is no way to obtain the name of the generator function from a Generator, so the following does not set any labels:

import { fetch, withLabels } from 'effection';

export function *fetchWeekDay(timezone) {
  let response = yield fetch(`http://worldclockapi.com/api/json/${timezone}/now`);
  let time = yield response.json();
  return time.dayOfTheWeek;
}

We do our best to infer the name, but as you can see it is not always possible for this reason it can be better to set the name label explicitly so there is no question as to whether it will show up.