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computed-proxy

computed-proxy

NPM version build status Downloads js-standard-style experimental

Computed properties with JavaScript Proxy.

Examples

const computed = require('computed-proxy')
 
const person = computed({
  lastName: 'Robinson Young',
  fullName: computed.property('firstName', 'lastName', {
    get (key, previous) {
      return `${this.firstName} ${this.lastName}`
    }
  })
})
 
person.firstName = 'Kyle'
console.log(person.fullName) // Kyle Robinson Young 
 
person.firstName = 'Crystal'
console.log(person.fullName) // Crystal Robinson Young 

With Arrays

const computed = require('computed-proxy')
 
const restaurant = computed({
  food: ['sushi'],
  menu: computed.property('food', {
    get (key, previous) {
      return this.food.join('')
    }
  })
})
 
console.log(restaurant.menu) // sushi 
 
restaurant.food.push('steak')
console.log(restaurant.menu) // sushi, steak 

With Nested Properties

const computed = require('computed-proxy')
 
const profile = computed({
  person: computed({
    name: 'Kyle',
    age: 34
  }),
  howOld: computed.property('person.name', 'person.age', {
    get (key, previous) {
      return `${this.person.name} is ${this.person.age} years old`
    }
  })
})
 
console.log(profile.howOld) // Kyle is 34 years old 
 
profile.person.name = 'Crystal'
profile.person.age = 33
console.log(profile.howOld) // Crystal is 33 years old 

With Properties Nested in Arrays

const computed = require('computed-proxy')
 
const restaurant = computed({
  food: [
    computed({ name: 'sushi', price: 50 })
  ],
  menu: computed.property('food.name', 'food.price', {
    get (key, previous) {
      return this.food.map(function (item) {
        return `${item.name} costs ${item.price}`
      }).join('')
    }
  })
})
 
console.log(restaurant.menu) // sushi costs 50 
 
restaurant.food.push(computed({ name: 'steak', price: 60 }))
console.log(restaurant.menu) // sushi costs 50, steak costs 60 
 
restaurant.food[0].price = 70
console.log(restaurant.menu) // sushi costs 70, steak costs 60 

Volatile

Mark properties as .volatile() to compute them on every get:

const computed = require('computed-proxy')
 
const person = computed({
  firstName: 'Kyle',
  lastName: 'Robinson Young',
  fullName: computed.property({
    get () {
      return `${this.firstName} ${this.lastName}`
    }
  }).volatile()
})
 
person.firstName = 'Crystal'
console.log(person.fullName) // Crystal Robinson Young 

Manually Trigger a Binding

If you want to manually mark a property to recompute on next get use .notifyPropertChange():

const computed = require('computed-proxy')
 
const person = computed({
  firstName: 'Kyle',
  lastName: 'Robinson Young',
  fullName: computed.property('lastName', {
    get (key, previous) {
      return `${this.firstName} ${this.lastName}`
    }
  })
})
 
console.log(person.fullName) // Kyle Robinson Young 
 
person.firstName = 'Crystal'
// Since fullName isnt bound to firstName, the get doesn't recompute 
console.log(person.fullName) // Kyle Robinson Young 
 
person.notifyPropertChange('fullName')
console.log(person.fullName) // Crystal Robinson Young 

Read Only By Default

All properties are read only by default and will throw an error if you try and set them. If you want your property to be settable, provide a set function:

const computed = require('computed-proxy')
 
const person = computed({
  firstName: 'Kyle',
  lastName: 'Robinson Young',
  upperName: computed.property('firstName', 'lastName', {
    get (key, previous) {
      return `${this.firstName} ${this.lastName}`.toUpperCase()
    },
    set (key, val, previous) {
      return val.toUpperCase()
    }
  })
})
 
console.log(person.upperName) // KYLE ROBINSON YOUNG 
 
person.upperName = 'somebody else'
console.log(person.upperName) // SOMEBODY ELSE 

Shim

In an environment that doesn't support Proxy? Shim it by including this in your code:

require('computed-proxy/shim')

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license

(c) 2017 Kyle Robinson Young. MIT License