How to disable a button when an input is empty?

reactjs

I'm new to React. I'm trying to disable a button when an input field is empty. What is the best approach in React for this?

I'm doing something like the following:

<input ref="email"/>

<button disabled={!this.refs.email}>Let me in</button>

Is this correct?

It's not just duplication of the dynamic attribute, because I'm also curious about transferring/checking the data from one element to another.

You'll need to keep the current value of the input in state (or pass changes in its value up to a parent via a callback function, or sideways, or <your app's state management solution here> such that it eventually gets passed back into your component as a prop) so you can derive the disabled prop for the button.

Example using state:

<meta charset="UTF-8">
<script src="https://fb.me/react-0.13.3.js"></script>
<script src="https://fb.me/JSXTransformer-0.13.3.js"></script>
<div id="app"></div>
<script type="text/jsx;harmony=true">void function() { "use strict";

var App = React.createClass({
  getInitialState() {
    return {email: ''}
  },
  handleChange(e) {
    this.setState({email: e.target.value})
  },
  render() {
    return <div>
      <input name="email" value={this.state.email} onChange={this.handleChange}/>
      <button type="button" disabled={!this.state.email}>Button</button>
    </div>
  }
})

React.render(<App/>, document.getElementById('app'))

}()</script>

Using constants allows to combine multiple fields for verification:

class LoginFrm extends React.Component {
  constructor() {
    super();
    this.state = {
      email: '',
      password: '',
    };
  }
  
  handleEmailChange = (evt) => {
    this.setState({ email: evt.target.value });
  }
  
  handlePasswordChange = (evt) => {
    this.setState({ password: evt.target.value });
  }
  
  handleSubmit = () => {
    const { email, password } = this.state;
    alert(`Welcome ${email} password: ${password}`);
  }
  
  render() {
    const { email, password } = this.state;
    const enabled =
          email.length > 0 &&
          password.length > 0;
    return (
      <form onSubmit={this.handleSubmit}>
        <input
          type="text"
          placeholder="Email"
          value={this.state.email}
          onChange={this.handleEmailChange}
        />
        
        <input
          type="password"
          placeholder="Password"
          value={this.state.password}
          onChange={this.handlePasswordChange}
        />
        <button disabled={!enabled}>Login</button>
      </form>
    )
  }
}

ReactDOM.render(<LoginFrm />, document.body);

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<body>


</body>

Another way to check is to inline the function, so that the condition will be checked on every render (every props and state change)

const isDisabled = () => 
  // condition check

This works:

<button
  type="button"
  disabled={this.isDisabled()}
>
  Let Me In
</button>

but this will not work:

<button
   type="button"
   disabled={this.isDisabled}
>
  Let Me In
</button>

const Example = () => {
  
const [value, setValue] = React.useState("");

function handleChange(e) {
    setValue(e.target.value);
  }

return (


<input ref="email" value={value} onChange={handleChange}/>
<button disabled={!value}>Let me in</button> 

);

}
 
export default Example;

How to disable a button when an input is empty?

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