Analyze the usage and principles of Vue's provide and inject

1. The parent component provides the parameters to be passed to the child component provide() {
    return {
      listType: this.listType,
    }
  }
2. Subcomponent usage:
inject: ['listType'],

inject:{
  listType:{
  from:"par"//provide the defined name default:1
  }
}

export function provide<T>(key: InjectionKey<T> | string | number, value: T) {
  if (!currentInstance) {
    if (__DEV__) {
      warn(`provide() can only be used inside setup().`)
    
    }
  } else {
    //Get the provides of the current component. The default instance inherits the provides object of the parent class. let provides = currentInstance.provides
    //Use the parent provided object as a prototype to create your own provided object const parentProvides =
      currentInstance.parent && currentInstance.parent.provides
    if (parentProvides === provides) {
      provides = currentInstance.provides = Object.create(parentProvides)
    }
    provides[key as string] = value
  }
}
​

export function inject(
  key: InjectionKey<any> | string,
  defaultValue?: unknown,
  treatDefaultAsFactory = false
) {
  //Get the current component instance const instance = currentInstance || currentRenderingInstance
  if (instance) {
  //Get provides
    const provides =
      instance.parent == null
        ? instance.vnode.appContext && instance.vnode.appContext.provides
        : instance.parent.provides
​
    if (provides && (key as string | symbol) in provides) {
      //If the key exists, return directly provides[key as string]
    } else if (arguments.length > 1) {
      //If the key does not exist, set the default value and return the default value directly return treatDefaultAsFactory && isFunction(defaultValue)
        ? defaultValue.call(instance.proxy)
        : defaultValue
    } else if (__DEV__) {
      //If none of them are found, warn(`injection "${String(key)}" not found.`)
    }
  } else if (__DEV__) {
    warn(`inject() can only be used inside setup() or functional components.`)
  }
}
​