notify-js

A simplified global or private notification channel for values that happened in the past, and those that will happen in the future. Related blog entry.

API

There are 2 main methods such .that(type[, any1[, any2[, ...]]]) and .when(type[, callback]), plus 3 extra helpers such .drop(type, callback), .all(type, callback), and .new().

notify.that(type[, ...])

This method is useful to notify about a generic channel.

// whenever it happens ...
navigator.geolocation.getCurrentPosition(info => {
  // ... notify anyone asking for 'geo:position'
  notify.that('geo:position', info);
});
 
// equivalent shortcut, will resolve
// with the first argument
navigator.geolocation.getCurrentPosition(
  notify.that('geo:position')
);
 
// NodeJS API compatible
fs.readFile(
  'package.json',
  notify.that('fs:package.json')
);

notify.that(type) and Promises

This method can also be used as middleware, passing along whatever first argument it receives.

// middleware
connectToDb
  // resolves and returns the value
  .then(notify.that('db:connected'))
  .then(readDatabaseInfo);

notify.when(type[, callback])

Usable both through callbacks or as Promise, the .when method asks for a channel and resolves it once available.

// using a callback
notify.when('geo:position', info => {
  console.log(info.coords);
});
 
// Promise based
notify.when('geo:position').then(info => {
  console.log(info.coords);
})

It doesn't matter if .when is used before or after a channel has been resolved, it will always pass along the last known resolved value.

// log on 'timer' channel (will log 123)
notify.when('timer', console.log);
 
// resolves the channel with value 1
notify.that('timer', 123);
 
setTimeout(() => {
  // log resolved 'timer' channel value
  // (will log 123)
  notify.when('timer', console.log);
}, 200);

Callback or Promise ?

If you are resolving older APIs like NodeJS require('fs').readFileSync, you probably want to use a callback because the resolution will pass along two arguments instead of one.

fs.readFile(
  'package.json',
  (err, blob) => {
    notify.that('fs:package.json', err, blob);
  }
);
 
notify.when('fs:package.json', (err, blob) => {
  if (err) return console.error(err);
  console.log(blob.toString());
});

As previously mentioned, you can still use the shortcut to resolve with all arguments once that happens.

fs.readFile(
  'package.json',
  notify.that('fs:package.json')
);

notify.drop(type, callback)

Usable only for callbacks registered via notify.when(type, callback), the .drop method avoid triggering the channel in the immediate present or future.

function log(value) {
  console.log(value);
}
 
// wait for it to happen
notify.when('happened', log);
 
// change your mind
notify.drop('happened', log);
 
// whenever it happens
// nothing will be logged
notify.that('happened', 'nope');

This method is particularly handy in conjunction of the notify.all(type, callback) method.

notify.all(type, callback)

In case you'd like to react every time a channel is updated, this method will register the callback and invoke it with the latest resolution each time.

// each position change
navigator.geolocation.watchPosition(
  // update with latest info
  notify.that('geo:position')
);
 
 
// react to all position changes
notify.all(
  'geo:position',
 
  // tracker
  info => {
    console.log(info.coords);
  }
);

Registered callbacks can be dropped through the notify.drop(type, callback) method.

notify.new()

There are basically two ways to have a private notification channel:

• using a private Symbol as channel, like in notify.when(privateSymbol).then(log)
• create a local version of the notifier that will share nothing with the main one, like in const notifyPVT = notify.new();

Which file ?

Browsers could use the minified version, otherwise there is a node module which is also available via npm as npm install notify-js.

Compatibility

This library is compatible with every JS engine since ES3, both browser and server, but a Promise polyfill might be needed to use Promise based patterns.