Vue 2源码阅读 Provide Inject 依赖注入详解

export function initInjections(vm: Component) {
  const result = resolveInject(vm.$options.inject, vm)
  if (result) {
    toggleObserving(false)
    Object.keys(result).forEach(key => {
      if (__DEV__) {
        defineReactive(vm, key, result[key], () => warn(''))
      } else {
        defineReactive(vm, key, result[key])
      }
    })
    toggleObserving(true)
  }
}
export function resolveInject(inject: any, vm: Component): Record<string, any> | undefined | null {
  if (inject) {
    const result = Object.create(null)
    const keys = hasSymbol ? Reflect.ownKeys(inject) : Object.keys(inject)

    for (let i = 0; i < keys.length; i++) {
      const key = keys[i]
      if (key === '__ob__') continue
      const provideKey = inject[key].from
      if (provideKey in vm._provided) {
        result[key] = vm._provided[provideKey]
      } else if ('default' in inject[key]) {
        const provideDefault = inject[key].default
        result[key] = isFunction(provideDefault) ? provideDefault.call(vm) : provideDefault
      } else if (__DEV__) {
        warn('')
      }
    }
    return result
  }
}

export function initProvide(vm: Component) {
  const provideOption = vm.$options.provide
  if (provideOption) {
    const provided = isFunction(provideOption) ? provideOption.call(vm) : provideOption
    if (!isObject(provided)) {
      return
    }
    const source = resolveProvided(vm)
    
    const keys = hasSymbol ? Reflect.ownKeys(provided) : Object.keys(provided)
    for (let i = 0; i < keys.length; i++) {
      const key = keys[i]
      Object.defineProperty(
        source,
        key,
        Object.getOwnPropertyDescriptor(provided, key)!
      )
    }
  }
}
export function resolveProvided(vm: Component): Record<string, any> {
  const existing = vm._provided
  const parentProvides = vm.$parent && vm.$parent._provided
  if (parentProvides === existing) {
    return (vm._provided = Object.create(parentProvides))
  } else {
    return existing
  }
}