vue/changes.md

Live doc. Subject to change anytime before 0.11 release.

Table of Contents

• Instantiation process
• New Scope Inheritance Model
• Instance Option changes
• Instance methods change
• Computed Properties API Change
• Directive API change
• Interpolation change
• Config API change
• Transition API change
• Events API change
• Two Way filters
• Block logic control
• Misc

Instantiation process

Breaking

If no el option is provided at instantiation, Vue will no longer auto-create an empty div for you. In this case, the instance is considered to be in "unmounted" state. Data will be observed, but no DOM compilation will happen until the new instance method $mount has been explicitly called.

var vm = new Vue({ data: {a:1} }) // only observes the data
vm.$mount('#app') // actually compile the DOM

// in comparison, this will compile instantly just like before.
var vm = new Vue({ el: '#app', data: {a: 1} })

New Scope Inheritance Model

Breaking

In the previous version, nested Vue instances do not have prototypal inheritance of their data scope. Although you can access parent data properties in templates, you need to explicitly travel up the scope chain with this.$parent in JavaScript code or use this.$get() to get a property on the scope chain. The expression parser also needs to do a lot of dirty work to determine the correct scope the variables belong to.

In the new model, we provide a scope inehritance system similar to Angular, in which you can directly access properties that exist on parent scopes. The major difference is that setting a primitive value property on a child scope WILL affect that on the parent scope! Because all data properties in Vue are getter/setters, so setting a property with the same key as parent on a child will not cause the child scope to create a new property shadowing the parent one, but rather it will just invoke the parent's setter function. See the example here.

The result of this model is a much cleaner expression evaluation implementation. All expressions can simply be evaluated against the vm.

By default, all child components DO NOT inherit the parent scope. Only anonymous instances created in v-repeat and v-if inherit parent scope by default. This avoids accidentally falling through to parent properties when you didn't mean to. If you want your component to explicitly inherit parent scope, use the inherit:true option.

Instance Option changes

• #### el and data for component definitions

Breaking

When used in component definitions and in Vue.extend(), the el, and data options now only accept a function that returns the per-instance value. For example:

  var MyComponent = Vue.extend({
    el: function () {
      var el = document.createElement('p')
      // you can initialize your element here.
      // you can even return a documentFragment to create
      // a block instance.
      el.className = 'content'
      return el
    },
    data: function () {
      // similar to ReactComponent.getInitialState
      return {
        a: {
          b: 123
        }
      }
    }
  })

• #### new option: events.

When events are used extensively for cross-vm communication, the ready hook can get kinda messy. The new events option is similar to its Backbone equivalent, where you can declaratiely register a bunch of event listeners. You can also use it to register hook listeners.

  var vm = new Vue({
    events: {
      'hook:created': function () {
        console.log('created!')
      },
      greeting: function (msg) {
        console.log(msg)
      },
      // can also use a string for methods
      bye: 'sayGoodbye'
    },
    methods: {
      sayGoodbye: function () {
        console.log('goodbye!')
      }
    }
  })
  // -> created!
  vm.$emit('greeting', 'hi!')
  // -> hi!
  vm.$emit('bye')
  // -> goodbye!

• #### new option: inherit.

Default: false.

Whether to inherit parent scope data. Set it to true if you want to create a component that inherits parent scope. By default, inside a component's template you won't be able to bind to data on parent scopes. When this is set to true, you will be able to:

1. bind to parent scope properties in the component template
2. directly access parent properties on the component instance itself, via prototypal inheritance.

• #### new option: mixins.

The mixins option accepts an array of mixin objects. These mixin objects can contain instance options just like normal instance objects, and they will be merged against the eventual options using the same merge logic in Vue.extend. e.g. If your mixin contains a created hook and the component itself also has one, both functions will be called.

  var mixin = {
    created: function () { console.log(2) }
  }
  var vm = new Vue({
    created: function () { console.log(1) },
    mixins: [mixin]
  })
  // -> 1
  // -> 2

• #### removed options:

Breaking

• parent

  This option has been removed. To create a child instance that inherits parent scope, use var child = parent.$addChild(options, [contructor]).

• lazy

  The lazy option is removed because this does not belong at the vm level. Users should be able to configure individual v-model instances to be lazy or not.

The following are also removed, use el with a function instead:

• id
• tagName
• className

• attributes

• hook changes

Breaking

• hook usage change: created

  In the past, you could do this.something = 1 inside the created hook to add observed data to the instance. Now the hook is called after the data observation, so if you wish to add additional data to the instance you should use the new $add and $delete API methods.

• hook usage change: ready

  The new ready hook now is only fired after the instance is compiled and inserted into the document for the first time. For a equivalence of the old ready hook, use the new compiled hook.

• new hook: beforeCompile

  This new hook is introduced to accompany the separation of instantiation and DOM mounting. It is called right before the DOM compilation starts and this.$el is available, so you can do some pre-processing on the element here.

• new hook: compiled

  The compiled hook indicates the element has been fully compiled based on initial data. However this doesn't indicate if the element has been inserted into the DOM yet. This is essentially the old ready hook.

• renamed hook: afterDestroy -> destroyed

Instance methods change

• vm.$watch

  • Expression watching

  vm.$watch can now accept an expression:

  vm.$watch('a + b', function (newVal, oldVal) {
    // do something
  })
  

  • Deep watching

  (Breaking) A change from 0.11 is that $watch now by default only fires when the identity of the watched value changes. If you want the watcher to also fire the callback when a nested value changes, pass in the third optional deep argument:

  vm.$watch('someObject', callback, true)
  vm.someObject.nestedValue = 123
  // callback is fired
  

  • Immediate invocation

  By default the callback only fires when the value changes. If you want it to be called immediately with the initial value, use the fourth optional immediate argument:

  vm.$watch('a', callback, false, true)
  // callback is fired immediately with current value of `a`
  

  • Unwatching

  (Breaking) $unwatch has been removed. $watch now also returns an unregister function:

  var unwatch = vm.$watch('a', cb)
  // later, teardown the watcher
  unwatch()
  

• vm.$get

vm.$get now accepts expressions:

  var value = vm.$get('a + b')

• New methods

  • vm.$add and vm.$delete

  Explicitly add/remove properties from the ViewModel. Observed objects are augmented with these two methods too. Use these only when needed - the best practice is to define all your data fields at instantiation, even with a null value.

  • vm.$eval

  Evaluate an expression that can also include filters.

  var value = vm.$eval('msg | uppercase')
  

  • vm.$interpolate

  Evalutate a piece of template string.

  var markup = vm.$interpolate('<p>{{msg | uppercase}}</p>')
  

  • vm.$log

  Log the current instance data as a plain object, which is more console-inspectable than a bunch of getter/setters. Also accepts an optional key.

  vm.$log() // logs entire ViewModel data
  vm.$log('item') // logs vm.item
  

Computed Properties API Change

Breaking

$get and $set is now simply get and set:

computed: {
  fullName: {
    get: function () {},
    set: function () {}
  }
}

Directive API change

• #### Dynamic literals

Literal directives can now also be dynamic via bindings like this:

  <div v-component="{{test}}"></div>

When test changes, the component used will change! This essentially replaces the old v-view directive.

When authoring literal directives, you can now provide an update() function if you wish to handle it dynamically. If no update() is provided the directive will be treated as a static literal and only evaluated once.

Note that v-component is the only directive that supports this.

• #### Directive params

Some built-in directives now checks for additional attribute params to trigger special behavior.

• v-model

  v-model now will check lazy attribute for lazy model update, and will check number attribute to know if it needs to convert the value into Numbers before writing back to the model.

  When used on a <select> element, v-model will check for an options attribute, which should be an keypath/expression that points to an Array to use as its options. The Array can contain plain strings, or contain objects.

  The object can be in the format of {label:'', value:''}. This allows you to have the option displayed differently from its underlying value:

  [
    { label: 'A', value: 'a' },
    { label: 'B', value: 'b' }
  ]
  

  Will render:

  <select>
    <option value="a">A</option>
    <option value="b">B</option>
  </select>
  

  Alternatively, the object can contain an options Array. In this case it will be rendered as an <optgroup>:

  [
    { label: 'A', options: ['a', 'b']},
    { label: 'B', options: ['c', 'd']}
  ]
  

  Will render:

  <select>
    <optgroup label="A">
      <option>a</option>
      <option>b</option>
    </optgroup>
    <optgroup label="B">
      <option>c</option>
      <option>d</option>
    </optgroup>
  </select>
  

• v-component

  When used as a dynamic component, it will check for the keep-alive attribute. When keep-alive is present, already instantiated components will be cached. This is useful when you have large, nested view components and want to maintain the state when switching views.

• v-repeat

  One of the questions I've asked about is how v-repeat does the array diffing and what happens if we swap the array with a fresh array grabbed from an API end point. In 0.10 because the objects are different, all instances have to been re-created. In 0.11 we introduce the trackby attribute param. If each of your data objects in the array has a unique id, we can use that id to reuse existing instances when the array is swapped.

  For example, if we have the data in the following format:

  items: [
    { _id: 1, ... },
    { _id: 2, ... },
    { _id: 3, ... }
  ]
  

  In your template you can do:

  <li v-repeat="items" trackby="_id">...</li>
  

  Later on when you swap items with a different array, even if the objects it contains are new, as long as they have the same trackby id we can still efficiently reuse existing instances.

• Usage change for v-with

In 0.10 and earlier, v-with creates a two-way binding between the parent and child instance. In 0.11, it no longer creates a two-way binding but rather facilitates a unidirectional data flow from parent to child.

For example:

  <div v-component="test" v-with="childKey:parentKey">{{childKey}}</div>

Here when you do this.a = 123 in the child, the child's view will update, but the parent's scope will remain unaffected. When parent.parentKey changes again, it will overwrite child.childKey.

• #### New directive: v-el

Similar to v-ref, but instead stores a reference to a DOM Node in vm.$$. For the reasoning behind the addition see this thread.

• #### New directive option: twoWay

This option indicates the directive is two-way and may write back to the model. Allows the use of this.set(value) inside directive functions.

• #### Removed directive option: isEmpty

Interpolation change

• (Breaking) Text bindings will no longer automatically stringify objects. Use the new json filter which gives more flexibility in formatting.

• One time interpolations

  <span>{{* hello }}</span>
  

One time interpolations do not need to set up watchers and can improve initial rendering performance. If you know something's not going to change, make sure to use this new feature. Example:

Config API change

Breaking

Instead of the old Vue.config() with a heavily overloaded API, the config object is now available globally as Vue.config, and you can simply change its properties:

// old
// Vue.config('debug', true)

// new
Vue.config.debug = true

• #### config.prefix change

Config prefix now should include the hyphen: so the default is now v- and if you want to change it make sure to include the hyphen as well. e.g. Vue.config.prefix = "data-".

• #### config.delimiters change

In the old version the interpolation delimiters are limited to the same base character (i.e. ['{','}'] translates into {{}} for text and {{{}}} for HTML). Now you can set them to whatever you like (*almost), and to indicate HTML interpolation, simply wrap the tag with one extra outer most character on each end. Example:

  Vue.config.delimiters = ['(%', '%)']
  // tags now are (% %) for text
  // and ((% %)) for HTML

• Note you still cannot use < or > in delimiters because Vue uses DOM-based templating.

• New config option: proto

Be default, Vue.js alters observed data objects' __proto__ when available for faster method interception/augmentation. This is perfectly fine when your data objects are plain JSON-derived objects. However if you want to use Vue's observation on object created with custom prototypes (e.g. from constructors), you can set Vue.config.proto = false to prohibit this behavior.

Transition API Change

Breaking

• no more distinctions between v-transition, v-animation or v-effect;
• no more configuring enter/leave classes in Vue.config;
• Vue.effect has been replaced with Vue.transition, the effects option has also been replaced by transitions.

With v-transition="my-transition", Vue will:

1. Try to find a transition definition object registered either through Vue.transition(id, def) or passed in with the transitions option, with the id "my-transition". If it finds it, it will use that definition object to perform the custom JavaScript based transition.

2. If no custom JavaScript transition is found, it will automatically sniff whether the target element has CSS transitions or CSS animations applied, and add/remove the classes as before.

3. If no transitions/animations are detected, the DOM manipulation is executed immediately instead of hung up waiting for an event.

• #### JavaScript transitions API change

Now more similar to Angular:

  Vue.transition('fade', {
    beforeEnter: function (el) {
      // a synchronous function called right before the
      // element is inserted into the document.
      // you can do some pre-styling here to avoid FOC.
    },
    enter: function (el, done) {
      // element is already inserted into the DOM
      // call done when animation finishes.
      $(el)
        .css('opacity', 0)
        .animate({ opacity: 1 }, 1000, done)
      // optionally return a "cancel" function
      // to clean up if the animation is cancelled
      return function () {
        $(el).stop()
      }
    },
    leave: function (el, done) {
      // same as enter
      $(el)
        .animate({ opacity: 0 }, 1000, done)
      return function () {
        $(el).stop()
      }
    }
  })

Events API change

Now if an event handler return false, it will stop event propagation for $dispatch and stop broadcasting to children for $broadcast.

var a = new Vue()
var b = new Vue({
  parent: a
})
var c = new Vue({
  parent: b
})

a.$on('test', function () {
  console.log('a')
})
b.$on('test', function () {
  console.log('b')
  return false
})
c.$on('test', function () {
  console.log('c')
})
c.$dispatch('test')
// -> 'c'
// -> 'b'

Two Way filters

If a filter is defined as a function, it is treated as a read filter by default - i.e. it is applied when data is read from the model and applied to the DOM. You can now specify write filters as well, which are applied when writing to the model, triggered by user input. Write filters are only triggered on two-way bindings like v-model.

Vue.filter('format', {
  read: function (val) {
    return val + '!'
  },
  write: function (val, oldVal) {
    return val.match(/ok/) ? val : oldVal
  }
})

Block logic control

One limitation of flow control direcitves like v-repeat and v-if is that they can only be used on a single element. Now you can use them to manage a block of content by using them on a <template> element that wraps the content you want managed:

items: [
  {
    title: 'title-1',
    subtitle: 'subtitle-1',
    content: 'content-1'
  },
  {
    title: 'title-2',
    subtitle: 'subtitle-2',
    content: 'content-2'
  }
]

<template v-repeat="item:items">
  <h2>{{item.title}}</h2>
  <p>{{item.subtitle}}</p>
  <p>{{item.content}}</p>
</template>

Rendered result:

<!--v-block-start-->
<h2>title-1</h2>
<p>subtitle-1</p>
<p>content-1</p>
<!--v-block-end-->
<!--v-block-start-->
<h2>title-2</h2>
<p>subtitle-2</p>
<p>content-2</p>
<!--v-block-end-->

Misc

• When there are inline values on input elements bound with v-model, e.g. <input value="hi" v-model="msg">, the inline value will be used as the inital value. If the vm comes with default data, it will be overwritten by the inline value. Same for selected attribute on <option> elements.