freeCodeCamp/curriculum/challenges/espanol/03-front-end-libraries/react/create-a-controlled-input.md

---
id: 5a24c314108439a4d4036178
title: Create a Controlled Input
challengeType: 6
forumTopicId: 301385
dashedName: create-a-controlled-input
---

# --description--

Your application may have more complex interactions between `state` and the rendered UI. For example, form control elements for text input, such as `input` and `textarea`, maintain their own state in the DOM as the user types. With React, you can move this mutable state into a React component's `state`. The user's input becomes part of the application `state`, so React controls the value of that input field. Typically, if you have React components with input fields the user can type into, it will be a controlled input form.

# --instructions--

The code editor has the skeleton of a component called `ControlledInput` to create a controlled `input` element. The component's `state` is already initialized with an `input` property that holds an empty string. This value represents the text a user types into the `input` field.

First, create a method called `handleChange()` that has a parameter called `event`. When the method is called, it receives an `event` object that contains a string of text from the `input` element. You can access this string with `event.target.value` inside the method. Update the `input` property of the component's `state` with this new string.

In the render method, create the `input` element above the `h4` tag. Add a `value` attribute which is equal to the `input` property of the component's `state`. Then add an `onChange()` event handler set to the `handleChange()` method.

When you type in the input box, that text is processed by the `handleChange()` method, set as the `input` property in the local `state`, and rendered as the value in the `input` box on the page. The component `state` is the single source of truth regarding the input data.

Last but not least, don't forget to add the necessary bindings in the constructor.

# --hints--

`ControlledInput` should return a `div` element which contains an `input` and a `p` tag.

```js
assert(
  Enzyme.mount(React.createElement(ControlledInput))
    .find('div')
    .children()
    .find('input').length === 1 &&
    Enzyme.mount(React.createElement(ControlledInput))
      .find('div')
      .children()
      .find('p').length === 1
);
```

The state of `ControlledInput` should initialize with an `input` property set to an empty string.

```js
assert.strictEqual(
  Enzyme.mount(React.createElement(ControlledInput)).state('input'),
  ''
);
```

Typing in the input element should update the state and the value of the input, and the `p` element should render this state as you type.

```js
async () => {
  const waitForIt = (fn) =>
    new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250));
  const mockedComponent = Enzyme.mount(React.createElement(ControlledInput));
  const _1 = () => {
    mockedComponent.setState({ input: '' });
    return waitForIt(() => mockedComponent.state('input'));
  };
  const _2 = () => {
    mockedComponent
      .find('input')
      .simulate('change', { target: { value: 'TestInput' } });
    return waitForIt(() => ({
      state: mockedComponent.state('input'),
      text: mockedComponent.find('p').text(),
      inputVal: mockedComponent.find('input').props().value
    }));
  };
  const before = await _1();
  const after = await _2();
  assert(
    before === '' &&
      after.state === 'TestInput' &&
      after.text === 'TestInput' &&
      after.inputVal === 'TestInput'
  );
};
```

# --seed--

## --after-user-code--

```jsx
ReactDOM.render(<ControlledInput />, document.getElementById('root'))
```

## --seed-contents--

```jsx
class ControlledInput extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      input: ''
    };
    // Change code below this line

    // Change code above this line
  }
  // Change code below this line

  // Change code above this line
  render() {
    return (
      <div>
        { /* Change code below this line */}

        { /* Change code above this line */}
        <h4>Controlled Input:</h4>
        <p>{this.state.input}</p>
      </div>
    );
  }
};
```

# --solutions--

```jsx
class ControlledInput extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      input: ''
    };
    this.handleChange = this.handleChange.bind(this);
  }
  handleChange(event) {
    this.setState({
      input: event.target.value
    });
  }
  render() {
    return (
      <div>
        <input
          value={this.state.input}
          onChange={this.handleChange} />
        <h4>Controlled Input:</h4>

        <p>{this.state.input}</p>
      </div>
    );
  }
};
```