React Passing Props to Second-level Children

Question

I faced the problem of passing props while coding in React. Yes, I have seen this issue before, but this time it's a second level-children component and things are a bit weird. My code (comments along the way):

class EditForm extends React.Component {
  handleSubmit = (event, idx) => {
    event => event.preventDefault();
      postData('/', {idx: idx})
    .then(data => {if (data.success) {window.location = '/';}});
    console.log(idx);          // results printed from here
  }

  render() {
    return (
      <Form
        onFinish={() => this.handleSubmit(idx)}                 // output 1
        onFinish={() => this.handleSubmit(this.props.idx)}      // output 2
      >
      </Form>
    );
  }
}

class UpdateModal extends React.Component {
  render() {
    return (
      <Modal>
        <EditForm idx={ this.props.idx } />             // value is still not undefined        
      </Modal>
    );
  }
}

Outputs:

// 1
useForm.js:766 ReferenceError: idx is not defined
// 2
undefined

Can anyone please explain why I can't pass the props two times in a row? As a matter of fact, the values are still valid when they are in UpdateModal but is gone somehow afterward.

Thanks in advance.

Answer 1

You should pass in the event object to your handlers:

class EditForm extends React.Component {
  handleSubmit = (event, idx) => {
    event => event.preventDefault();
      postData('/', {idx: idx})
    .then(data => {if (data.success) {window.location = '/';}});
    console.log(idx);          // results printed from here
  }

  render() {
    return (
      <Form
        onFinish={(event) => this.handleSubmit(event, idx)}                 // output 1
        onFinish={(event) => this.handleSubmit(event, this.props.idx)}      // output 2
      >
      </Form>
    );
  }
}

class UpdateModal extends React.Component {
  render() {
    return (
      <Modal>
        <EditForm idx={ this.props.idx } />             // value is still not undefined        
      </Modal>
    );
  }
}

Answer 2

class EditForm extends React.Component { constructor(props) { super(props); } // ... } class UpdateModal extends React.Component { constructor(props) { super(props); } // ... } // <EditForm idx={this.state.idx}></EditForm> // <UpdateModal idx={this.state.idx}></UpdateModal>