MobX decorators

Several helper MobX decorators

MobX 5 is not supported yet

1. Installation
2. Decorators

• @setter
• @toggle
• @observe
• @intercept
• @_interceptReads
• @save
• @allObservable

3. Changelog

Installation

npm install --save mobx-decorators

You also should use some transpiler (like babel).

npm install --save-dev @babel/plugin-proposal-decorators

Decorators

@setter

@setter
@setter(name)
@setter(name, constValue)
@setter(transformFn: value =>)
@setter(name, transformFn: value =>)

Create setter for property with setProperty or custom name.

If constValue provided this value will be set every time setter called. You can also provide transform function.

With transformFn function you can change value that will be set.

import {observable} from 'mobx'
import {setter} from 'mobx-decorators'

class User {
  @setter @observable loggedIn = false;
}

const user = new User();
user.setLoggedIn(true); // user.loggedIn = true

class User {
  @setter('updateLoggedIn')
  @observable loggedIn = false;
}

const user = new User();
user.updateLoggedIn(true); // user.loggedIn = true

class User {
  @setter('login', true)
  @setter('logout', false)
  @observable loggedIn = false;
}

const user = new User();
user.login(); // user.loggedIn = true
user.logout(); // user.loggedIn = false

class User {
  @setter(value => value && value.toUpperCase())
  @observable name;
}

const user = new User();
user.setName('Alice'); // user.name = 'ALICE'

@toggle

@toggle
@toggle(name)

Toggle boolean property (property = !property).

import {observable} from 'mobx'
import {toggle} from 'mobx-decorators'

class User {
  @toggle @observable loggedIn = false;
}

const user = new User();
user.toggleLoggedIn(); // user.loggedIn = !user.loggedIn

class User {
  @toggle('swapLoggedIn')
  @observable loggedIn = false;
}

const user = new User();
user.swapLoggedIn(); // user.loggedIn = !user.loggedIn

@observe

@observe(onChanged: change =>)
@observe(onChanged: change =>, invokeBeforeFirstAccess)

onChanged will be called after property change.

If invokeBeforeFirstAccess is true handler will be called one time before property first access (set or get).

More info can be found in mobx docs

import {observable} from 'mobx'
import {observe} from 'mobx-decorators'

class User {
  @observe(change => console.log(change.newValue))
  @setter @observable loggedIn = false;
}

const user = new User();
user.setLoggedIn(true); // console.log(true)

class User {
  @observe(change => console.log(change.newValue), true)
  @setter @observable loggedIn = false;
}

const user1 = new User();
const loggedIn = user.loggedIn; // console.log(false)
user1.setLoggedIn(true); // console.log(true)

const user2 = new User();
user2.setLoggedIn(true); // console.log(false)
                         // console.log(true)

@intercept

@intercept(onWillChange: change =>)

onWillChange will be called before property change. You can replace value or cancel change in handler.

More info can be found in mobx docs

import {observable} from 'mobx'
import {intercept} from 'mobx-decorators'

class User {
  @intercept(change => {
    change.newValue = 999;
    return change;
  })
  @setter @observable loginCount = 0;
}

const user = new User();
user.setLoginCount(1); // user.loginCount = 999;

class User {
  @intercept(change => null)
  @setter @observable loginCount = 0;
}

const user = new User();
user.setLoginCount(1); // user.loginCount = 0;

@_interceptReads

@_interceptReads(onRead: value =>)

interceptReads renamed in Mobx4 and look like will be deprecated

onRead will be called before property reading. You can transform value in handler.

More info can be found in mobx CHANGELOG

import {observable} from 'mobx'
import {_interceptReads} from 'mobx-decorators'

class User {
  @_interceptReads(value => value && value.toUpperCase())
  @observable name = 'Alice';
}

const user = new User();
console.log(user.name) // ALICE

@save

@save
@save({
  storage = defaultStorage(),
  storeName = store => store.storeName,
  serializer = {
    save: value => JSON.stringify(value),
    load: data => JSON.parse(data),
  },
  onLoaded = (store, property, value) => {},
  onSaved = (store, property, value) => {},
  onInitialized = (store, property, value) => {},
})
createSaveDecorator(baseOptions={})

(!) TypeScript: you can't use class property initializers (class F {prop = 1}) with @save decorator

@save decorator helps save and load observable value to/from permanent storage. Keep in mind @save is lazy decorator and loading will be started only after first property access. If you change property before or during loading than restored value will be ignored.

onLoaded callback will be called only if value is loaded from storage.
onSaved will be called after saving.
onInitialized will be called after loading attempt independent of the result.

By default values saved as json. In some cases (Date for example) you should provide serializer (see example with date).

You must define storeName property in store (see examples) or pass it as option. storeName option can be string or function.

Default storage is localStorage for browser, AsyncStorage for React Native and memory for other platforms. You can specify you own (localForage for example) by storage option. Storage must realize simple interface (functions are async or return Promise):

const MyStorage = {
  async getItem(key) {
    // return item
  },
  async setItem(key, value) {
    // save item
  }
}

If you need to pass the same options (storage for example) to @save decorator of several properties than you can use createSaveDecorator function.

import {observable} from 'mobx'
import {save, createSaveDecorator} from 'mobx-decorators'

class User {
  storeName = 'user';

  @save @observable loginCount;
}

const user = new User();
console.log(user.loginCount); // undefined
// @save will try to load loginCount from storage but
// loading is async (!) so value is still undefined here

class User {
  storeName = 'user';

  // storage contains 999 for loginCount property
  @save({
    onInitialized: (store, property, value) => {
      console.log(property, value); // 'loginCount', 999
      console.log(store.loginCount); // 999
    },
    onLoaded: (store, property, value) => {
      console.log(property, value); // 'loginCount', 999
      console.log(store.loginCount); // 999
    },
    onSaved: (store, property, value) => {
      console.log(property, value); // 1000
    }
  })
  @setter @observable loginCount;
}

const user = new User();
console.log(user.loginCount); // undefined, loading loginCount

// throw some time
console.log(user.loginCount); // 999

user.setLoginCount(1000); // 1000 will be saved to storage

class User {
  @save({
    storeName: 'user',
  })
  @observable loginCount;
  
  @save({
    storeName: 'group',
  })
  @observable group;
}

const user = new User();
console.log(user.loginCount); // undefined, loading loginCount
console.log(user.group); // undefined, loading group

class User {
  storeName = 'user';

  @save({
    serializer: {
      load: data => new Date(fromBSON(data)),
      save: value => toBSON(value),
    },
  })
  @observable lastLogin;
}

const user = new User();
console.log(user.lastLogin);

const mysave = createSaveDecorator({
  storage: MyOwnStorage,
  storeName: store => store.constructor.name,
});

class User {
  @mysave @observable loginCount;
  
  @save @observable name;
}

const user = new User();
console.log(user.loginCount);

const mysave = createSaveDecorator({
  storage: MyOwnStorage,
  storeName: 'user',
});

class User {
  @mysave({
    onInitialized: () => console.log('initialized')
  })
  @observable loginCount;
  
  @save @observable name;
}

const user = new User();
console.log(user.loginCount);

@allObservable

@allObservable
@allObservable({
  only,
  except = [],
})

Class decorator that makes all properties observable. Use only for whitelisting properties and except for blacklisting.

import {allObservable} from 'mobx-decorators'

@allObservable
class User {
  name = 'unknown';
  loginCount = 0;
}

@allObservable({only: ['loginCount']})
class User {
  name = 'unknown';
  loginCount = 0;
}

@allObservable({except: ['name']})
class User {
  name = 'unknown';
  loginCount = 0;
}