javascript - How to disable button in React.js

Question

I have this component:

import React from 'react';

export default class AddItem extends React.Component {

add() {
    this.props.onButtonClick(this.input.value);
    this.input.value = '';
}


render() {
    return (
        <div className="add-item">
            <input type="text" className="add-item__input" ref={(input) => this.input = input} placeholder={this.props.placeholder} />
            <button disabled={!this.input.value} className="add-item__button" onClick={this.add.bind(this)}>Add</button>
        </div>
    );
}

}

I want the button to be disabled when input value is empty. But the code above doesn't work. It says:

add-item.component.js:78 Uncaught TypeError: Cannot read property 'value' of undefined

pointing to disabled={!this.input.value}. What can I be doing wrong here? I'm guessing that perhaps ref isn't created yet when render method is executed. If, so what is the workararound?

Answer 1

Using refs is not best practice because it reads the DOM directly, it's better to use React's state instead. Also, your button doesn't change because the component is not re-rendered and stays in its initial state.

You can use setState together with an onChange event listener to render the component again every time the input field changes:

// Input field listens to change, updates React's state and re-renders the component.
<input onChange={e => this.setState({ value: e.target.value })} value={this.state.value} />

// Button is disabled when input state is empty.
<button disabled={!this.state.value} />

Here's a working example:

class AddItem extends React.Component {
  constructor() {
    super();
    this.state = { value: '' };
    this.onChange = this.onChange.bind(this);
    this.add = this.add.bind(this);
  }

  add() {
    this.props.onButtonClick(this.state.value);
    this.setState({ value: '' });
  }

  onChange(e) {
    this.setState({ value: e.target.value });
  }

  render() {
    return (
      <div className="add-item">
        <input
          type="text"
          className="add-item__input"
          value={this.state.value}
          onChange={this.onChange}
          placeholder={this.props.placeholder}
        />
        <button
          disabled={!this.state.value}
          className="add-item__button"
          onClick={this.add}
        >
          Add
        </button>
      </div>
    );
  }
}

ReactDOM.render(
  <AddItem placeholder="Value" onButtonClick={v => console.log(v)} />,
  document.getElementById('View')
);

<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>
<div id='View'></div>