How to call react function from external JavaScript file

You have some logic here that doesn't completely make sense.

In your class, you define file_input_html, which returns a component.

Then, in fn_test, you call attempt to call that function (which doesn't work -- I'll address that in a minute), but you don't do anything with the output.

The article that you linked to tells you how to get a ref to a component (eg the div in this case) -- not the actual Contact, which doesn't have a property named file_input_html anyway -- that's just a function you declared inside its scope.

What I'm assuming you want to happen (based on the code you shared) is for your external javascript file to be able to tell your component to render a form with a certain ID and then be able to get a reference to it. Here's an example of how to do this (it's a little convoluted, but it's a funny situation):

const { useState } = React

const App = (props) => {
  const [formId, setFormId] = useState(2)
  
  useEffect(() => {
    window.alterFormId = setFormId
  },[])
  
  return (<div id={"form" + formId} ref={(ourComponent) => {window.ourComponent = ourComponent}}>
     Text {formId} 
  </div>);
}

setTimeout(() => { 
  window.alterFormId(8);
  setTimeout(() => {
    console.log(window.ourComponent)
    window.ourComponent.innerText = "Test"
  }, 20)
}, 1000)

ReactDOM.render(<App />,
document.getElementById("root"))

What's happening here:

1. In useEffect, I set alterFormId on window so that it can be used outside of the React files
2. Using the technique you linked to, I get a ref to the div that's created. Note that I'm setting the ID here as well, based on the state of formId
3. The setTimeout function at the end tests all this: a) It waits until the first render (the first setTimeout) and then calls alterFormId b) Then, it waits again (just 20ms) so that the next run loop has happened and the React component has re-rendered, with the new formId and reference c) From there, it calls a method on the div just to prove that the reference works.

I'm not exactly sure of your use case for all this and there are probably easier ways to architect things to avoid these issues, but this should get you started.

안녕하세요. 자바스크립트로 흐름만 알려드리겠습니다

아래 코드들을 참고해보세요.

iframe간 통신은

window.postMessage API와 window.addEventListener('message', handler) 메시지 수신 이벤트 리스너 로 구현할 수있습니다. 보안관련해서도 방어로직이 몇줄 필요합니다(origin 체크 등)

in parent

import React from 'react';

export function Parent () {
  const childRef = React.useRef(null);
  const handleMessage = (ev) => {
    // 방어로직들
    if (check ev.origin, check ev.source, ....) {

      return false;
    }

    console.log('handleMessage(parent)', ev)
  }
  React.useEffect(() => {

    window.addEventListener('message', handleMessage);

    // clean memory
    return () => {
      window.removeEventListener('message', handleMessage);
    }
  })

  return (
    <div>
      <iframe ref="childRef" src="child_src" id="iframe"></iframe>
    </div>
  )
}

in child

import React from 'react';

export function Iframe () {
  const handleMessage = (ev) => {
    console.log('handleMessage(child)', ev)
  }
  const messagePush = () => {
    window.parent.postMessage({ foo: 'bar' }, 'host:port')
  }

  React.useEffect(() => {
    window.addEventListener('message', handleMessage);

    // clean memory
    return () => {
      window.removeEventListener('message', handleMessage);
    }
  })

  return (
    <div>
      <button onClick={messagePush}>Push message</button>
    </div>
  )
}