/* *******************************************************************************************
 * GLOBAL CONFIG
 * Vue.config is an object containing Vue’s global configurations.
 * You can modify its properties listed below before bootstrapping your application.
 * https://vuejs.org/v2/api/#Global-Config
 * ******************************************************************************************* */


// Configure whether to allow vue-devtools inspection
Vue.config.devtools = true

// Enable component init, compile, render and patch performance tracing in the browser devtool timeline.
Vue.config.performance = true

// Prevent the production tip on Vue startup.
Vue.config.productionTip = false

// Suppress all Vue logs and warnings
Vue.config.silent = false

// Make Vue ignore custom elements defined outside of Vue
Vue.config.ignoredElements = [
  'my-custom-web-component',
  'another-web-component',
  /^ion-/
]

// Define custom key alias(es) for v-on.
Vue.config.keyCodes = {
  v: 86,
  f1: 112,
  // camelCase won`t work
  mediaPlayPause: 179,
  // instead you can use kebab-case with double quotation marks
  "media-play-pause": 179,
  up: [38, 87]
}

// Assign a handler for uncaught errors during component render function and watchers. 
Vue.config.errorHandler = function (err, vm, info) {
  // handle error
  // `info` is a Vue-specific error info, e.g. which lifecycle hook
  // the error was found in. Only available in 2.2.0+
}

// Define custom merging strategies for options
Vue.config.optionMergeStrategies._my_option = function (parent, child, vm) {
  return child + 1
}

// Assign a custom handler for runtime Vue warnings.
// Note this only works during development and is ignored in production.
Vue.config.warnHandler = function (msg, vm, trace) {
  // `trace` is the component hierarchy trace
}


/* *******************************************************************************************
 * GLOBAL API
 * https://vuejs.org/v2/api/#Global-API
 * ******************************************************************************************* */


Vue.version                        // Provides the installed version of Vue as a string.

Vue.extend(options)                // Create a “subclass” of the base Vue constructor.
Vue.mixin( mixin )                 // Apply a mixin globally, which affects every Vue instance created afterwards.
Vue.nextTick([callback, context])  // Defer the callback to be executed after the next DOM update cycle.
Vue.use(plugin)                    // Install a Vue.js plugin. If the plugin is an Object, it must expose an install method.

Vue.set(target, key, value)        // Set a property on an object. If the object is reactive, ensure the property is created as a reactive property and trigger view updates.
Vue.delete(target, key)            // Delete a property on an object. If the object is reactive, ensure the deletion triggers view updates.

// Register or retrieve a global directive.
Vue.directive('my-directive', {
  bind: function () {},
  inserted: function () {},
  update: function () {},
  componentUpdated: function () {},
  unbind: function () {}
})

// Register (function directive)
Vue.directive('my-directive', function () {
  // This will be called as `bind` and `update`
})

// Getter, return the directive definition if registered
var myDirective = Vue.directive('my-directive')

// Register a global filter
Vue.filter('my-filter', function (value) { })

// Getter, return the filter if registered
var myFilter = Vue.filter('my-filter')

// Register an extended constructor
Vue.component('my-component', Vue.extend({ }))

// Register an options object (automatically call Vue.extend)
Vue.component('my-component', { })

// Retrieve a registered component (always return constructor)
var MyComponent = Vue.component('my-component')

Vue.compile(template)  // Compiles a template string into a render function


/* *******************************************************************************************
 * OPTIONS > DATA
 * https://vuejs.org/v2/api/#Options-Data
 * ******************************************************************************************* */


new Vue({
  // A list/hash of attributes that are exposed to accept data from the parent component.
  // It has an Array-based simple syntax and an alternative Object-based syntax that allows
  // advanced configurations such as type checking, custom validation and default values.
  props: {
    height: Number,
    age: {
      type: Number,
      default: 0,
      required: true,
      validator: function (value) {
        return value >= 0
      }
    }
  },

  // Primarily intended to make unit testing easier
  propsData: {
    age: 12
  },

  // The data object for the Vue instance.
  // Vue will recursively convert its properties into getter/setters to make it “reactive”. 
  // Note: you should not use an arrow function with the data property
  data () {
    return {
      a: 1,
      b: 2
    }
  },

  // Computed properties to be mixed into the Vue instance.
  // All getters and setters have their this context automatically bound to the Vue instance.
  // Computed properties are cached, and only re-computed on reactive dependency changes.
  // Note that if a certain dependency is out of the instance’s scope (i.e. not reactive),
  // the computed property will not be updated.
  computed: {
    // Note: you should not use an arrow function to define a computed property.
    aDouble: function () {
      return this.a * 2
    },
    aPlus: {
      get: function () {
        return this.a + 1
      },
      set: function (v) {
        this.a = v - 1
      }
    }
  },

  // An object where keys are expressions to watch and values are the corresponding callbacks.
  // The value can also be a string of a method name, or an Object that contains additional options.
  // The Vue instance will call $watch() for each entry in the object at instantiation.
  watch: {
    // Note: you should not use an arrow function to define a watcher.
    a: function (val, oldVal) {
      console.log('new: %s, old: %s', val, oldVal)
    },
    // String method name
    b: 'someMethod',
    // Deep watcher
    c: {
      handler: function (val, oldVal) { /* ... */ },
      deep: true
    },
    // The callback will be called immediately after the start of the observation
    d: {
      handler: function (val, oldVal) { /* ... */ },
      immediate: true
    }
  },

  // Methods to be mixed into the Vue instance. You can access these methods directly on the VM instance,
  // or use them in directive expressions. All methods will have their this context automatically bound to
  // the Vue instance.
  methods: {
    // Note: you should not use an arrow function to define a method.
    plus () {
      this.a++
    }
  }
})


/* *******************************************************************************************
 * OPTIONS > DOM
 * https://vuejs.org/v2/api/#Options-DOM
 * ******************************************************************************************* */


new Vue({
  // Provide the Vue instance an existing DOM element to mount on.
  // It can be a CSS selector string or an actual HTMLElement.
  // After the instance is mounted, the resolved element will be accessible as vm.$el.
  el: '#example',

  // A string template to be used as the markup for the Vue instance.
  // The template will replace the mounted element.
  // Any existing markup inside the mounted element will be ignored,
  // unless content distribution slots are present in the template.
  // If the string starts with # it will be used as a querySelector and
  // use the selected element’s innerHTML as the template string. This
  // allows the use of the common <script type="x-template"> trick to include templates.
  template: `
    <div class="checkbox-wrapper" @click="check">
      <div :class="{ checkbox: true, checked: checked }"></div>
      <div class="title">{{ title }}</div>
    </div>
  `,

  // An alternative to string templates allowing you to leverage the full programmatic power of JavaScript.
  // The render function receives a createElement method as it’s first argument used to create VNodes.
  // If the component is a functional component, the render function also receives an extra argument context,
  // which provides access to contextual data since functional components are instance-less.
  render (createElement) {
    // create kebabCase id
    var headingId = getChildrenTextContent(this.$slots.default)
    .toLowerCase()
    .replace(/\W+/g, '-')
    .replace(/(^\-|\-$)/g, '')

    return createElement(
      'h' + this.level,
      [
        createElement('a', {
          attrs: {
            name: headingId,
            href: '#' + headingId
          }
        }, this.$slots.default)
      ]
    )
  },

  // Provide an alternative render output when the default render function encounters an error.
  // The error will be passed to renderError as the second argument.
  // This is particularly useful when used together with hot-reload.
  renderError (createElement, err) {
    return createElement('pre', { style: { color: 'red' }}, err.stack)
  }
})


/* *******************************************************************************************
 * OPTIONS > LIFECYCLE HOOKS
 * https://vuejs.org/v2/api/#Options-Lifecycle-Hooks
 * ******************************************************************************************* */


// All lifecycle hooks automatically have their this context bound to the instance,
// so that you can access data, computed properties, and methods. This means you should not
// use an arrow function to define a lifecycle method (e.g. created: () => this.fetchTodos()).
// The reason is arrow functions bind the parent context, so this will not be the Vue instance as
// you expect and this.fetchTodos will be undefined.

new Vue({
  // Called synchronously immediately after the instance has been initialized,
  // before data observation and event/watcher setup.
  beforeCreate () {
    console.log('The instance has been initialized')
  },

  // Called synchronously after the instance is created. At this stage, the instance has
  // finished processing the options which means the following have been set up: data observation,
  // computed properties, methods, watch/event callbacks. However, the mounting phase has not been
  // started, and the $el property will not be available yet.
  created () {
    console.log('The instance has been created')
  },

  // Called right before the mounting begins: the render function
  // is about to be called for the first time.
  beforeMount () {
    console.log('The instance is about to be mounted')
  },

  // Called after the instance has been mounted, where el is replaced by the newly created vm.$el.
  // If the root instance is mounted to an in-document element, vm.$el will also be in-document when
  // mounted is called.
  mounted () {
    console.log('The instance has been mounted')

    // Note that mounted does not guarantee that all child components have also been mounted.
    // If you want to wait until the entire view has been rendered, you can use vm.$nextTick
    // inside of mounted:
    this.$nextTick(function () {
      // Code that will run only after the
      // entire view has been rendered
    })
  },

  // Called when the data changes, before the virtual DOM is re-rendered and patched.
  // You can perform further state changes in this hook and they will not trigger additional re-renders.
  // This hook is not called during server-side rendering.  
  beforeUpdate () {
    console.log('The instance is about to be re-rendered and patched')
  },

  // The component’s DOM will have been updated when this hook is called, so you can perform DOM-dependent
  // operations here. However, in most cases you should avoid changing state inside the hook. To react
  // to state changes, it’s usually better to use a computed property or watcher instead.
  updated () {
    console.log('The instance has been re-rendered and patched')

    // Note that updated does not guarantee that all child components have also been re-rendered.
    // If you want to wait until the entire view has been re-rendered, you can use vm.$nextTick
    // inside of updated:
    this.$nextTick(function () {
      // Code that will run only after the
      // entire view has been re-rendered
    })
  },

  // Called when a kept-alive component is activated.
  activated () {
    console.log('Component activated')
  },

  // Called when a kept-alive component is deactivated.  
  deactivated () {
    console.log('Component deactivated')
  },

  // Called right before a Vue instance is destroyed.
  // At this stage the instance is still fully functional.
  beforeDestroy () {
    console.log('The instance is about to be destroyed')
  },

  // Called after a Vue instance has been destroyed.
  // When this hook is called, all directives of the Vue instance have been unbound,
  // all event listeners have been removed, and all child Vue instances have also been destroyed.  
  destroyed () {
    console.log('The instance has been destroyed')
  },

  // Called when an error from any descendent component is captured.
  // The hook receives three arguments: the error, the component instance that triggered the error,
  // and a string containing information on where the error was captured.
  // The hook can return false to stop the error from propagating further.
  errorCaptured (error, vm, info) {
    console.log(`The error (${error}) has been captured for ${vm}: ${info}`)

    // An errorCaptured hook can return false to prevent the error from propagating further.
    // This is essentially saying “this error has been handled and should be ignored.”
    // It will prevent any additional errorCaptured hooks or the global config.errorHandler
    // from being invoked for this error.
    return false
  },
})


/* *******************************************************************************************
 * OPTIONS > ASSETS
 * https://vuejs.org/v2/api/#Options-Assets
 * ******************************************************************************************* */


new Vue({
  // A hash of directives to be made available to the Vue instance.
  directives: {
    myDirective: {
      // Called only once, when the directive is first bound to the element.
      // This is where you can do one-time setup work.
      bind: function (el, binding, vnode, oldVnode) {
        console.log('The directive is first bound to the element.')
      },

      // Called when the bound element has been inserted into its parent node
      // (this only guarantees parent node presence, not necessarily in-document).
      inserted: function (el, binding, vnode, oldVnode) {
        console.log('The bound element has been inserted into its parent node.')
      },

      // Called after the containing component’s VNode has updated, but possibly before its
      // children have updated. The directive’s value may or may not have changed, but you can
      // skip unnecessary updates by comparing the binding’s current and old values (see below
      // on hook arguments).
      update: function (el, binding, vnode, oldVnode) {
        console.log('The component VNode has updated.')
      },

      // Called after the containing component’s VNode and the VNodes of its children have updated.
      componentUpdated: function (el, binding, vnode, oldVnode) {
        console.log('The component’s VNode and the VNodes of its children have updated.')
      },
      
      // Called only once, when the directive is unbound from the element.
      unbind: function (el, binding, vnode, oldVnode) {
        console.log('The directive is unbound from the element.')
      },
    }
  },

  // A hash of filters to be made available to the Vue instance.
  filters: {
    myFilter: function (value) {
      console.log('Do your computations and return something to display.')
    }
  }
})


/* *******************************************************************************************
 * OPTIONS > COMPOSITION
 * https://vuejs.org/v2/api/#Options-Composition
 * ******************************************************************************************* */


new Vue({
  // Specify the parent instance for the instance to be created. Establishes a parent-child
  // relationship between the two. The parent will be accessible as this.$parent for the child,
  // and the child will be pushed into the parent’s $children array.
  parent: vueInstance,

  // The mixins option accepts an array of mixin objects. These mixin objects can contain instance
  // options like normal instance objects, and they will be merged against the eventual options
  // using the same option merging 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.
  // Mixin hooks are called in the order they are provided, and called before the component’s own hooks.
  mixins: [mixin],

  // Allows declaratively extending another component (could be either a plain options object or a
  // constructor) without having to use Vue.extend. This is primarily intended to make it easier to
  // extend between single file components. This is similar to mixins, the difference being that
  // the component’s own options takes higher priority than the source component being extended.
  extends: ObjectOrFunction,
})


/* *******************************************************************************************
 * OPTIONS > MISC
 * https://vuejs.org/v2/api/#Options-Lifecycle-Hooks
 * ******************************************************************************************* */


new Vue({
  // Allow the component to recursively invoke itself in its template.
  // Note that when a component is registered globally with Vue.component(), the global ID is
  // automatically set as its name.
  // Another benefit of specifying a name option is debugging. Named components result in more
  // helpful warning messages. Also, when inspecting an app in the vue-devtools, unnamed components
  // will show up as <AnonymousComponent>, which isn’t very informative. By providing the name
  // option, you will get a much more informative component tree.
  name: 'myComponent',

  // Change the plain text interpolation delimiters.
  delimiters: ['${', '}'],

  // Causes a component to be stateless (no data) and instanceless (no this context). They are
  // only a render function that returns virtual nodes making them much cheaper to render.
  functional: true,

  // By default, parent scope attribute bindings that are not recognized as props will
  // “fallthrough” and be applied to the root element of the child component as normal HTML
  // attributes. When authoring a component that wraps a target element or another component,
  // this may not always be the desired behavior. By setting inheritAttrs to false, this default
  // behavior can be disabled. The attributes are available via the $attrs instance property
  // (also new in 2.4) and can be explicitly bound to a non-root element using v-bind.
  // Note: this option does not affect class and style bindings.  
  inheritAttrs: true,

  // When set to true, will preserve and render HTML comments found in templates. The default
  // behavior is discarding them.
  comments: true,
})


/* *******************************************************************************************
 * INSTANCE PROPERTIES
 * https://vuejs.org/v2/api/#Instance-Properties
 * ******************************************************************************************* */


// The data object that the Vue instance is observing.
// The Vue instance proxies access to the properties on its data object.
vm.$data

// An object representing the current props a component has received.
// The Vue instance proxies access to the properties on its props object.
vm.$props

// The root DOM element that the Vue instance is managing.
vm.$el

// The instantiation options used for the current Vue instance.
// This is useful when you want to include custom properties in the options:
vm.$options

// The parent instance, if the current instance has one.
vm.$parent

// The root Vue instance of the current component tree.
// If the current instance has no parents this value will be itself.
vm.$root

// The direct child components of the current instance.
// Note there’s no order guarantee for $children, and it is not reactive.
// If you find yourself trying to use $children for data binding,
// consider using an Array and v-for to generate child components,
// and use the Array as the source of truth.
vm.$children

// Used to programmatically access content distributed by slots.
// Each named slot has its own corresponding property (e.g. the contents of slot="foo" will
// be found at vm.$slots.foo). The default property contains any nodes not included in a named slot.
// Accessing vm.$slots is most useful when writing a component with a render function.
vm.$slots

// Used to programmatically access scoped slots. For each slot, including the default one, the
// object contains a corresponding function that returns VNodes.
// Accessing vm.$scopedSlots is most useful when writing a component with a render function.
vm.$scopedSlots

// An object that holds child components that have ref registered.
vm.$refs

// Whether the current Vue instance is running on the server.
vm.$isServer

// Contains parent-scope attribute bindings (except for class and style) that are not recognized
// (and extracted) as props. When a component doesn’t have any declared props, this essentially
// contains all parent-scope bindings (except for class and style), and can be passed down to an
// inner component via v-bind="$attrs" - useful when creating higher-order components.
vm.$attrs

// Contains parent-scope v-on event listeners (without .native modifiers).
// This can be passed down to an inner component via v-on="$listeners" - useful when creating
// higher-order components.
vm.$listeners


/* *******************************************************************************************
 * INSTANCE METHODS > DATA
 * https://vuejs.org/v2/api/#Instance-Methods-Data
 * ******************************************************************************************* */


// Watch an expression or a computed function on the Vue instance for changes.
// The callback gets called with the new value and the old value.
// The expression only accepts dot-delimited paths.
// For more complex expressions, use a function instead.
var unwatch = vm.$watch('a.b.c', function (newVal, oldVal) {
  // do something
}, {
  // To also detect nested value changes inside Objects, you need to pass in deep: true
  // in the options argument. Note that you don’t need to do so to listen for Array mutations.
  deep: true,

  // Passing in immediate: true in the option will trigger the callback immediately with the
  // current value of the expression:
  immediate: true
})

// later, teardown the watcher
unwatch()

// This is the alias of the global Vue.set.
vm.$set(target,key, value)

// This is the alias of the global Vue.delete.
vm.$delete(target, key)


/* *******************************************************************************************
 * INSTANCE METHODS > EVENTS
 * https://vuejs.org/v2/api/#Instance-Methods-Events
 * ******************************************************************************************* */


// Listen for a custom event on the current vm. Events can be triggered by vm.$emit.
// The callback will receive all the additional arguments passed into these event-triggering methods.
vm.$on(event, callback)

// Listen for a custom event, but only once.
// The listener will be removed once it triggers for the first time.
vm.$once(event, callback)

// Remove custom event listener(s).
// If no arguments are provided, remove all event listeners;
// If only the event is provided, remove all listeners for that event;
// If both event and callback are given, remove the listener for that specific callback only.
vm.$off([event, callback])

// Trigger an event on the current instance.
// Any additional arguments will be passed into the listener’s callback function.
vm.$emit(event, […args])


/* *******************************************************************************************
 * INSTANCE METHODS > LIFECYCLE
 * https://vuejs.org/v2/api/#Instance-Methods-Lifecycle
 * ******************************************************************************************* */


// If a Vue instance didn’t receive the el option at instantiation, it will be in “unmounted”
// state, without an associated DOM element. vm.$mount() can be used to manually start the mounting
// of an unmounted Vue instance.
vm.$mount([elementOrSelector])

// Force the Vue instance to re-render. Note it does not affect all child components,
// only the instance itself and child components with inserted slot content.
vm.$forceUpdate()

// Defer the callback to be executed after the next DOM update cycle.
// Use it immediately after you’ve changed some data to wait for the DOM update.
// This is the same as the global Vue.nextTick, except that the callback’s this context is
// automatically bound to the instance calling this method.
vm.$nextTick([callback])

// Completely destroy a vm. Clean up its connections with other existing vms, unbind all its
// directives, turn off all event listeners.
// Triggers the beforeDestroy and destroyed hooks.
vm.$destroy()


/* *******************************************************************************************
 * DIRECTIVES
 * https://vuejs.org/v2/api/#Directives
 * ******************************************************************************************* */


// <!-- Updates the element’s textContent. -->
// <!-- If you need to update the part of textContent, you should use {{ Mustache }} interpolations. -->

// <span v-text="msg"></span>


// <!-- Updates the element’s innerHTML. Note that the contents are inserted as plain HTML -->
// <!-- they will not be compiled as Vue templates. If you find yourself trying to compose templates -->
// <!-- using v-html, try to rethink the solution by using components instead. -->

// <div v-html="html"></div>


// <!-- Toggle’s the element’s display CSS property based on the truthy-ness of the expression value. -->
// <!-- This directive triggers transitions when its condition changes. -->

// <div v-show="condition"></div>


// <!-- Conditionally render the element based on the truthy-ness of the expression value. -->
// <!-- The element and its contained directives / components are destroyed and re-constructed -->
// <!-- during toggles. If the element is a <template> element, its content will be extracted as -->
// <!-- the conditional block. This directive triggers transitions when its condition changes. -->

// <div v-if="condition"></div>
// <div v-else-if="anotherCondition"></div>
// <div v-else></div>


// <!-- Render the element or template block multiple times based on the source data. -->
// <!-- The directive’s value must use the special syntax alias in expression to provide an alias -->
// <!-- for the current element being iterated on: -->

// <div v-for="item in items">{{ item.text }}</div>


// <!-- Alternatively, you can also specify an alias for the index (or the key if used on an Object): -->

// <div v-for="(item, index) in items"></div>
// <div v-for="(val, key) in object"></div>
// <div v-for="(val, key, index) in object"></div>


// <!-- Attaches an event listener to the element. The event type is denoted by the argument. -->
// <!-- The expression can be a method name, an inline statement, or omitted if there are modifiers present. -->

// .stop:                                           Call event.stopPropagation().
// .prevent:                                        Call event.preventDefault().
// .capture:                                        Add event listener in capture mode.
// .self:                                           Only trigger handler if event was dispatched from this element.
// .{keyCode | keyAlias}:                           Only trigger handler on certain keys.
// .native:                                         Listen for a native event on the root element of component.
// .once:                                           Trigger handler at most once.
// .left:                                           (2.2.0+) only trigger handler for left button mouse events.
// .right:                                          (2.2.0+) only trigger handler for right button mouse events.
// .middle:                                         (2.2.0+) only trigger handler for middle button mouse events.
// .passive:                                        (2.3.0+) attaches a DOM event with { passive: true }.

// Method handler:                                  <button v-on:click="doThis"></button>
// Object syntax (2.4.0+):                          <button v-on="{ mousedown: onMouseDown, mouseup: onMouseUp }"></button>
// Inline statement:                                <button v-on:click="doThat('hello', $event)"></button>
// Shorthand:                                       <button @click="doThis"></button>
// Stop propagation:                                <button @click.stop="doThis"></button>
// Prevent default:                                 <button @click.prevent="doThis"></button>
// Prevent default without expression:              <form @submit.prevent></form>
// Chain modifiers:                                 <button @click.stop.prevent="doThis"></button>
// Key modifier using keyAlias:                     <input @keyup.enter="onEnter">
// Key modifier using keyCode:                      <input @keyup.13="onEnter">
// The click event will be triggered at most once:  <button v-on:click.once="doThis"></button>


// <!-- Dynamically bind one or more attributes, or a component prop to an expression. -->
// <!-- When used to bind the class or style attribute, it supports additional value types such as -->
// <!-- Array or Objects. See linked guide section below for more details. -->

// .prop:                                                    Bind as a DOM property instead of an attribute.
// .camel:                                                   (2.1.0+) transform the kebab-case attribute name into camelCase.
// .sync:                                                    (2.3.0+) a syntax sugar that expands into a v-on handler for updating the bound value.

// Bind an attribute:                                        <img v-bind:src="imageSrc">
// Shorthand:                                                <img :src="imageSrc">
// With inline string concatenation:                         <img :src="'/path/to/images/' + fileName">
// Class binding:                                            <div :class="{ red: isRed }"></div>
// Style binding:                                            <div :style="{ fontSize: size + 'px' }"></div>
// Binding an object of attributes                           <div v-bind="{ id: someProp, 'other-attr': otherProp }"></div>
// DOM attribute binding with prop modifier:                 <div v-bind:text-content.prop="text"></div>
// Prop binding. "prop" must be declared in my-component:    <my-component :prop="someThing"></my-component>
// Pass down parent props in common with a child component:  <child-component v-bind="$props"></child-component>
// XLink:                                                    <svg><a :xlink:special="foo"></a></svg>


// <!-- Create a two-way binding on a form input element or a component. -->
// <!-- For detailed usage and other notes, see the Guide section linked below. -->

// .lazy:    Listen to change events instead of input
// .number:  Cast input string to numbers
// .trim:    Trim input

// <input v-model="message" placeholder="edit me">
// <textarea v-model="message" placeholder="add multiple lines"></textarea>
// <input type="checkbox" id="checkbox" v-model="checked">


// <!-- Skip compilation for this element and all its children. -->
// <!-- You can use this for displaying raw mustache tags. -->
// <!-- Skipping large numbers of nodes with no directives on them can also speed up compilation. -->

// <span v-pre>{{ this will not be compiled }}</span>


// <!-- This directive will remain on the element until the associated Vue instance finishes -->
// <!-- compilation. Combined with CSS rules such as [v-cloak] { display: none }, this directive -->
// <!-- can be used to hide un-compiled mustache bindings until the Vue instance is ready. -->

// <div v-cloak>{{ message }}</div>
// [v-cloak] { display: none; }


// <!-- Render the element and component once only. On subsequent re-renders, the element/component -->
// <!-- and all its children will be treated as static content and skipped. This can be used to -->
// <!-- optimize update performance. -->

// <span v-once>This will never change: {{msg}}</span>
// <my-component v-once :comment="msg"></my-component>


/* *******************************************************************************************
 * SPECIAL ATTRIBUTES
 * https://vuejs.org/v2/api/#Special-Attributes
 * ******************************************************************************************* */


// <!-- The key special attribute is primarily used as a hint for Vue’s virtual DOM algorithm to -->
// <!-- identify VNodes when diffing the new list of nodes against the old list. Without keys, Vue uses -->
// <!-- an algorithm that minimizes element movement and tries to patch/reuse elements of the same type -->
// <!-- in-place as much as possible. With keys, it will reorder elements based on the order change of -->
// <!-- keys, and elements with keys that are no longer present will always be removed/destroyed. -->

// <ul><li v-for="item in items" :key="item.id">...</li></ul>
// <transition><span :key="text">{{ text }}</span></transition>


// <!-- ref is used to register a reference to an element or a child component. The reference will be -->
// <!-- registered under the parent component’s $refs object. If used on a plain DOM element, the -->
// <!-- reference will be that element; if used on a child component, the reference will be component instance: -->

// <!-- vm.$refs.p will be the DOM node -->
// <p ref="p">hello</p>

// <!-- vm.$refs.child will be the child comp instance -->
// <child-comp ref="child"></child-comp>


// <!-- Used on content inserted into child components to indicate which named slot the content belongs to. -->
// <!-- Child markup: -->
// <header><slot name="header"></slot></header>
// <!-- Parent markup: -->
// <app-layout><h1 slot="header">Here might be a page title</h1></app-layout>


// <!-- Used for dynamic components and to work around limitations of in-DOM templates. -->
// <component :is="currentView"></component>