How to Avoid the \'Uncontrolled Input to Controlled Input Transition Error\' in ReactJS?

Uncontrolled Input to Controlled Input Transition Error in ReactJS

React warns against switching between uncontrolled and controlled input elements. This error typically occurs when an input field initially accepts user input freely (uncontrolled) and then the developer later attempts to control its value through state (controlled).

Code Snippet:

The error is illustrated by the following code:

<code class="javascript">constructor(props) {
  super(props);
  this.state = {
    fields: {},
    errors: {}
  }
}

onChange(field, e){
  let fields = this.state.fields;
  fields[field] = e.target.value;
  this.setState({fields});
}

render() {
  return(
    <div className="form-group">
      <input
        value={this.state.fields["name"]}
        onChange={this.onChange.bind(this, "name")}
        className="form-control"
        type="text"
        refs="name"
        placeholder="Name *"
      />
    </div>
  )
}</code>

Root Cause:

In this code, the issue lies in the initial state where fields is initialized as an empty object. When the component first renders, this.state.fields.name is undefined, making the input an uncontrolled component. However, when the user enters a value, fields is updated, making the input controlled.

Possible Solutions:

To resolve this error, there are two options:

1. Initialize fields with a Default Value:

   Define fields in the initial state with a default value:

   <code class="javascript">this.state = {
     fields: {name: ''}
   }</code>

2. Use Short-circuit Evaluation:

   Use short-circuit evaluation in the value attribute to provide a default value when this.state.fields.name is undefined:

   <code class="javascript"><input value={this.state.fields.name || ''} /></code>

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