React `useImperativeHandle` Magic

Intro

I am a full-stack TypeScript developer and I've been learning the Elm language a lot recently. Will I switch to Elm? Definitely not. However, the learning process helped me understand and demand more things in React.

Today I will show you a React anti-pattern that will allow you to share state outside components. Why would you do this? Why not use a hook? etc. etc. I will show you an example with a small form.

Note: This is not a "real-world" example. In production env I am using this hook to create synchronized S3 File browser, but it might be too much for the sake of this article.

The Hook

So this combination of State and Callback is to connect the ref function later and listen when the ref changes:

import { useState, useCallback } from "react";

export const useImperativeRef = <T>() => {
  const [refState, setRefState] = useState<T>();
  const ref = useCallback((n: T | null) => {
    if (n) {
      setRefState(n);
    }
  }, []);
  return [refState, ref] as const;
};

The form

We don't need anything fancy for this example so we will use a simple form with 2 inputs:

import React, {
  useImperativeHandle,
  useState,
} from "react";


interface FormValues{
    username: string;
    password: string;
}

export interface MyFormHandle{
    values: FormValues
}

export const MyForm = React.forwardRef(({},ref: React.ForwardedRef<MyFormHandle>) => {
    const [values,setValues]  = useState<FormValues>({
        username: "",
        password: "",
    })
    useImperativeHandle(
        ref,
        () => ({
            values
        })
    )
    return <div>
        <input type="text" value={values.username} onChange={e => 
            setValues({
                ...values,
                username: e.target.value
            })
        } />
        <input type="password" value={values.password} onChange={e => 
            setValues({
                ...values,
                password: e.target.value
            })
        } />
    </div>
})

Using the form

Et voila! We can listen to state changes of components underneath:

export default () => {
    const [values,setRef] = useImperativeRef<MyFormHandle>()
    useEffect(() => {
        console.log(`Values changed!, Values: ${JSON.stringify(values,null,4)}`)
    }, [values])
    return <div>
        <MyForm ref={setRef} />
    </div>  
}

Of course, we can pass change functions and values, but let's be true - that's Yuck! In my opinion, this way is much more elegant and codeless in many cases.

Blog

React `useImperativeHandle` Magic

Tomek Poniatowicz

Intro

The Hook

The form

Using the form

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