An awesome Vue.js cheatsheet.
/* *******************************************************************************************
* 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>