Vue: Inject/Provide is not reactive

[ralphchristianeclipse]

Version

2.5.3

Reproduction link

https://codesandbox.io/s/7o2qp4l3z6

Steps to reproduce

Parent Component

    provide() {
      let reactive = {};

      Object.defineProperties(reactive, {
        challenge: {
          get: () => this.challenge
        }
      });

      return reactive;
    },

Child Component

inject: ["challenge"]

What is expected?

The challenge property should change when its parent this.challenge changes on the proxy

What is actually happening?

Not changing at all

---

The link provided is just an example how to reimplement what i'm really doing but that is the same code that i use

any ideas?

[posva]

Unfortunately, that's by design. you can hack around it using an object an referring to its children, but it's not recommended because it could break in future versions of Vue

[lehni]

I'd like to point out two possible solutions to this problem:

1. There is a plugin/mixin now by @LinusBorg to deal with this: https://github.com/LinusBorg/vue-reactive-provide
2. Instead of providing the actual computed property, you could provide a method that is to be used as a getter by the children that inject it to then get the property when needed:

// parent:
{
  provide() {
    return {
      $computedProperty: () => this.computedProperty
    }
  },

  computed: {
    computedProperty() {
      // Returns the result of some potentially reactive computation
    }
  }
}

// children:
{
  inject: [
    '$computedProperty'
  ],

  computed: {
    computedProperty() {
      return this.$computedProperty()
    }
  }
}

[LinusBorg]

That second trick is great, never thought of that!

[lehni]

@LinusBorg a function used as a tunnel / wormhole through the non-reactive JS space-continuum :)

[Tofandel]

@lehni
Just a small mistake, this is not accessible within the provide object you need to declare it like this for it to work

provide() {
    return {
        $computedProperty: () => this.computedProperty,
    };
  },

[lehni]

@Tofandel hmmm but you have the same code there as I do? And I'm using this in production, sure works for me...

[lehni]

@Tofandel never mind, I just noticed now that @posva edited my code to include your fix before I saw your post. I also have this version in my own use, not sure why I posted the object version above initially :)

[Tofandel]

@lehni Haha okay I thought you edited it so I was confused :p

[dmitry]

This must be added to the recipes or guides.

[cihad]

I have discovered new way:

// parent:
{
  provide() {
    const _this = this;

    return {
      get computedProperty () {
         return _this.computedProperty;
      }
    }
  },

  computed: {
    computedProperty() {
      // Returns the result of some potentially reactive computation
    }
  }
}

// children:
{
  inject: [
    'computedProperty'
  ],
}

You don't need computed method in children anymore.

[louisameline]

I discovered a flaw in @lehni 's trick today. Wrapping the object in a function triggers an error when the providing object gets unmounted I think, as if the injection briefly couldn't be resolved anymore:

[Vue warn]: Injection "$computedProperty" not found

This error doesn't happen when a plain object is passed.
I could circumvent it by providing a wrapped-wrapped (!) default value in the child component:

// children:
{
  inject: [
    '$computedProperty': {
      // you need to provide a default object that doesn't trigger errors
      // in your component when used
      default: () => () => {}
    }
  ],
  computed: {
    computedProperty() {
      return this.$computedProperty()
    }
  }
}

It feels dirty overall. We should probably avoid passing functions.
As a reminder, the Vue docs advise against inject/provide anyway, and just use props, even if it's more verbose.

@cihad I haven't been able to make your trick work, it's not reactive for me. And I needed two different names to avoid a loop: get computedProperty () { return _this.$computedProperty }

[sstern6]

It seems like the only way to get it to work is by providing a function, and then in the component it is injected in you need to create a computed prop and call the function like the example above.

Has there been any progress on opinions of how to tackle this? I dont want to prop drill or use state management. Provide/Inject seems like the best solution, but feels weird we need to hack around the cleanest solution.

Thoughts?