Options: State #

data #

A function that returns the initial reactive state for the component instance.

• 类型

  interface ComponentOptions {
    data?(
      this: ComponentPublicInstance,
      vm: ComponentPublicInstance
    ): object
  }
  

• 详细信息

  The function is expected to return a plain JavaScript object, which will be made reactive by Vue. After the instance is created, the original data object can be accessed as this.$data. The component instance also proxies all the properties found on the data object, so this.a will be equivalent to this.$data.a.

  Once observed, you can no longer add reactive properties to the root data object. It is therefore recommended to declare all root-level reactive properties upfront, before creating the instance.

  Properties that start with _ or $ will not be proxied on the component instance because they may conflict with Vue's internal properties and API methods. You will have to access them as this.$data._property.

  It is not recommend to return objects with their own stateful behavior like browser API objects and prototype properties. The returned object should ideally be a plain object that only represents the state of the component.

• 示例

  export default {
    data() {
      return { a: 1 }
    },
    created() {
      console.log(this.a) // 1
      console.log(this.$data) // { a: 1 }
    }
  }
  

  Note that if you use an arrow function with the data property, this won't be the component's instance, but you can still access the instance as the function's first argument:

  data: (vm) => ({ a: vm.myProp })
  

• 相关内容： Reactivity in Depth

props #

Declare the props of a component.

• 类型

  interface ComponentOptions {
    props?: ArrayPropsOptions | ObjectPropsOptions
  }
  
  type ArrayPropsOptions = string[]
  
  type ObjectPropsOptions = { [key: string]: Prop }
  
  type Prop<T = any> = PropOptions<T> | PropType<T> | null
  
  interface PropOptions<T> {
    type?: PropType<T>
    required?: boolean
    default?: T | ((rawProps: object) => T)
    validator?: (value: unknown) => boolean
  }
  
  type PropType<T> = { new (): T } | { new (): T }[]
  

  为了便于阅读，对类型进行了简化。

• 详细信息

  In Vue, all component props need to be explicitly declared. Component props can be declared in two forms:

  • Simple form using an array of strings
  • Full form using an object where each property key is the name of the prop, and the value is the prop's type (a constructor function) or advanced options.

  With object-based syntax, each prop can further defined the following options:

  • type: Can be one of the following native constructors: String, Number, Boolean, Array, Object, Date, Function, Symbol, any custom constructor function or an array of those. In development mode, Vue will check if a prop's value matches the declared type, and will throw a warning if it doesn't. See Prop Validation for more details.

    Also note that a prop with Boolean type affects its value casting behavior in both development and production. See Boolean Casting for more details.

  • default: Specifies a default value for the prop when it is not passed by the parent or has undefined value. Object or array defaults must be returned using a factory function. The factory function also receives the raw props object as the argument.

  • required: Defines if the prop is required. In a non-production environment, a console warning will be thrown if this value is truthy and the prop is not passed.

  • validator: Custom validator function that takes the prop value as the sole argument. In development mode, a console warning will be thrown if this function returns a falsy value (i.e. the validation fails).

• 示例

  Simple declaration:

  export default {
    props: ['size', 'myMessage']
  }
  

  Object declaration with validations:

  export default {
    props: {
      // type check
      height: Number,
      // type check plus other validations
      age: {
        type: Number,
        default: 0,
        required: true,
        validator: (value) => {
          return value >= 0
        }
      }
    }
  }
  

• 相关内容： Props

computed #

Declare computed properties to be exposed on the component instance.

• 类型

  interface ComponentOptions {
    computed?: {
      [key: string]: ComputedGetter<any> | WritableComputedOptions<any>
    }
  }
  
  type ComputedGetter<T> = (
    this: ComponentPublicInstance,
    vm: ComponentPublicInstance
  ) => T
  
  type ComputedSetter<T> = (
    this: ComponentPublicInstance,
    value: T
  ) => void
  
  type WritableComputedOptions<T> = {
    get: ComputedGetter<T>
    set: ComputedSetter<T>
  }
  

• 详细信息

  The option accepts an object where the key is the name of the computed property, and the value is either a computed getter, or an object with get and set methods (for writable computed properties).

  All getters and setters have their this context automatically bound to the component instance.

  Note that if you use an arrow function with a computed property, this won't point to the component's instance, but you can still access the instance as the function's first argument:

  export default {
    computed: {
      aDouble: (vm) => vm.a * 2
    }
  }
  

• 示例

  export default {
    data() {
      return { a: 1 }
    },
    computed: {
      // readonly
      aDouble() {
        return this.a * 2
      },
      // writable
      aPlus: {
        get() {
          return this.a + 1
        },
        set(v) {
          this.a = v - 1
        }
      }
    },
    created() {
      console.log(this.aDouble) // => 2
      console.log(this.aPlus) // => 2
  
      this.aPlus = 3
      console.log(this.a) // => 2
      console.log(this.aDouble) // => 4
    }
  }
  

• 相关内容： Computed Properties

methods #

Declare methods to be mixed into the component instance.

• 类型

  interface ComponentOptions {
    methods?: {
      [key: string]: (this: ComponentPublicInstance, ...args: any[]) => any
    }
  }
  

• 详细信息

  Declared methods can be directly accessed on the component instance, or used in template expressions. All methods have their this context automatically bound to the component instance, even when passed around.

  Avoid using arrow functions when declaring methods, as they will not have access to the component instance via this.

• 示例

  export default {
    data() {
      return { a: 1 }
    },
    methods: {
      plus() {
        this.a++
      }
    },
    created() {
      this.plus()
      console.log(this.a) // => 2
    }
  }
  

  为了便于阅读，对类型进行了简化。

• 详细信息

Declare watch callbacks to be invoked on data change.

• 类型

  interface ComponentOptions {
    watch?: {
      [key: string]: WatchOptionItem | WatchOptionItem[]
    }
  }
  
  type WatchOptionItem = string | WatchCallback | ObjectWatchOptionItem
  
  type WatchCallback<T> = (
    value: T,
    oldValue: T,
    onCleanup: (cleanupFn: () => void) => void
  ) => void
  
  type ObjectWatchOptionItem = {
    handler: WatchCallback | string
    immediate?: boolean // default: false
    deep?: boolean // default: false
    flush?: 'pre' | 'post' | 'sync' // default: 'pre'
    onTrack?: (event: DebuggerEvent) => void
    onTrigger?: (event: DebuggerEvent) => void
  }
  

  为了便于阅读，对类型进行了简化。

• 详细信息

  The watch option expects an object where keys are the reactive component instance properties to watch (e.g. properties declared via data or computed) — and values are the corresponding callbacks. The callback receives the new value and the old value of the watched source.

  In addition to a root-level property, The key can also be a simple dot-delimited path, e.g. a.b.c. Note that this usage does not support complex expressions - only dot-delimited paths are supported. If you need to watch complex data sources, this the imperative $watch() API instead.

  The value can also be a string of a method name (declared via methods), or an object that contains additional options. When using the object syntax, the callback should be declared under the handler field. Additional options include:

  • immediate: trigger the callback immediately on watcher creation. Old value will be undefined on the first call.
  • deep: force deep traversal of the source if it is an object or an array, so that the callback fires on deep mutations. See Deep Watchers.
  • flush: adjust the callback's flush timing. See Callback Flush Timing.
  • onTrack / onTrigger: debug the watcher's dependencies. See Watcher Debugging.

  Avoid using arrow functions when declaring watch callbacks as they will not have access to the component instance via this.

• 示例

  export default {
    data() {
      return {
        a: 1,
        b: 2,
        c: {
          d: 4
        },
        e: 5,
        f: 6
      }
    },
    watch: {
      // watching top-level property
      a(val, oldVal) {
        console.log(`new: ${val}, old: ${oldVal}`)
      },
      // string method name
      b: 'someMethod',
      // the callback will be called whenever any of the watched object properties change regardless of their nested depth
      c: {
        handler(val, oldVal) {
          console.log('c changed')
        },
        deep: true
      },
      // watching a single nested property:
      'c.d': function (val, oldVal) {
        // do something
      },
      // the callback will be called immediately after the start of the observation
      e: {
        handler(val, oldVal) {
          console.log('e changed')
        },
        immediate: true
      },
      // you can pass array of callbacks, they will be called one-by-one
      f: [
        'handle1',
        function handle2(val, oldVal) {
          console.log('handle2 triggered')
        },
        {
          handler: function handle3(val, oldVal) {
            console.log('handle3 triggered')
          }
          /* ... */
        }
      ]
    },
    methods: {
      someMethod() {
        console.log('b changed')
      },
      handle1() {
        console.log('handle 1 triggered')
      }
    },
    created() {
      this.a = 3 // => new: 3, old: 1
    }
  }
  

• 相关内容： Watchers

emits #

Declare the custom events emitted by the component.

• 类型

  interface ComponentOptions {
    emits?: ArrayEmitsOptions | ObjectEmitsOptions
  }
  
  type ArrayEmitsOptions = string[]
  
  type ObjectEmitsOptions = { [key: string]: EmitValidator | null }
  
  type EmitValidator = (...args: unknown[]) => boolean
  

• 详细信息

  Emitted events can be declared in two forms:

  • Simple form using an array of strings
  • Full form using an object where each property key is the name of the event, and the value is either null or a validator function.

  The validation function will receive the additional arguments passed to the component's $emit call. For example, if this.$emit('foo', 1) is called, the corresponding validator for foo will receive the argument 1. The validator function should return a boolean to indicate whether the event arguments are valid.

  Note that the emits option affects which event listeners received by the component are considered component event listeners vs. native DOM event listeners. A declared event's listener will not be added to the component's root element, and will be removed from the component's $attrs object. See Fallthrough Attributes for more details.

• 示例

  Array syntax:

  export default {
    emits: ['check'],
    created() {
      this.$emit('check')
    }
  }
  

  Object syntax:

  export default {
    emits: {
      // no validation
      click: null,
  
      // with validation
      submit: (payload) => {
        if (payload.email && payload.password) {
          return true
        } else {
          console.warn(`Invalid submit event payload!`)
          return false
        }
      }
    }
  }
  

• See also: Fallthrough Attributes

expose #

Declare exposed public properties when the component instance is accessed by a parent via template refs.

• 类型

  interface ComponentOptions {
    expose?: string[]
  }
  

• 详细信息

  By default, a component instance exposes all instance properties to the parent when accessed via $parent, $root, or template refs. This can be undesirable since a component most likely have internal state or methods that should be kept private to avoid tight coupling.

  The expose option expects a list of property name strings. When expose is used, only the properties explicitly listed will be exposed on the component's public instance.

  expose only affects user-defined properties - it does not filter out built-in component instance properties.

• 示例

  export default {
    // only `publicMethod` will be available on the public instance
    expose: ['publicMethod'],
    methods: {
      publicMethod() {
        // ...
      },
      privateMethod() {
        // ...
      }
    }
  }