Pier Pier - 4 months ago 16
Javascript Question

React: what's the proper way of passing a ref to a prop?

I'm trying to pass a ref of a component to another component. Since string refs are being deprecated I'm using callback refs.

So I have something similar to this:

<One ref={c => this.one = c}/>
<Two one={this.one}/>


The problem is that whenever I try to access
this.props.one
inside
Two
I get
undefined
.

I have even tried this on
Two
:

componentDidMount(){
setTimeout(()=>{
console.log(this.props.one);
},5000)
}


It seems the problem is that when the prop is created, the ref doesn't exist yet since it's created once
One
is mounted. But I don't know how to "refresh" the props on
Two
to get the ref to the mounted component.

So what's the proper way of passing a ref to another component?

Edit

Some users have suggested to encapsulate that logic in a higher component, which in itself renders those other child components.

The problem with that approach is that you can't create reusable logic and you have to repeat the same logic over and over in those encapsulating components.

Let's say you want to create a generic
<Form>
component which encapsulates the submit logic to your store, error checking, etc. And you do something like this:

<Form>
<Input/>
<Input/>
<Input/>
<Input/>
<SubmitButton/>
</Form>


In this example
<Form>
can't access the instances (and methods) of the children since
this.props.children
doesn't return those instances. It returns some list of pseudo components.

So how can you check if a certain
<Input/>
has detected a validation error without passing a ref?

You have to encapsulate those components in another component with the validation logic. For example in
<UserForm>
. But since each form is different the same logic has to be copied in
<CategoryForm>
,
<GoupForm>
, etc. This is terribly inefficient which is why I want to encapsulate the validation logic in
<Form>
and pass references of the
<Input>
components to
<Form>
.

Answer

In general the "ref" feature is an anti-pattern in React. It exists to enable side-effect driven development, however in order to benefit the most from the React way of programming you should try to avoid "refs" if possible.

As for your particular issue, passing a child a ref to it's sibling is a chicken vs. egg scenario. The ref callback is fired when the child is mounted, not during render which is why your example doesn't work. One thing you can try is pushing the ref into state and then reading from state into the other child. So:

<One ref={c => !this.state.one && this.setState({ one: c })}/>
<Two one={this.state.one}/>

Note: without the !this.state.one this will cause an infinite loop.

Here is a codepen example of this working (look at the console to see the sibling ref logged): http://codepen.io/anon/pen/pbqvRA