[javascript] How to disable button in React.js

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?

just Add:

<button disabled={this.input.value?"true":""} className="add-item__button" onClick={this.add.bind(this)}>Add</button>

I have had a similar problem, turns out we don't need hooks to do these, we can make an conditional render and it will still work fine.

<Button
    type="submit"
    disabled={
        name === "" || email === "" || password === "" ? true : false
    }
    fullWidth
    variant="contained"
    color="primary"
    className={classes.submit}>
    SignUP
</Button>

In HTML,

<button disabled/>
<buttton disabled="true">
<buttton disabled="false">
<buttton disabled="21">

All of them boils down to disabled="true" that is because it returns true for a non-empty string. Hence, in order to return false, pass a empty string in a conditional statement like this.input.value?"true":"".

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?"true":""} className="add-item__button" onClick={this.add.bind(this)}>Add</button>
        </div>
    );
}

this.input is undefined until the ref callback is called. Try setting this.input to some initial value in your constructor.

From the React docs on refs, emphasis mine:

the callback will be executed immediately after the component is mounted or unmounted

very simple solution for this is by using useRef hook

const buttonRef = useRef();

const disableButton = () =>{
  buttonRef.current.disabled = true; // this disables the button
 }

<button
className="btn btn-primary mt-2"
ref={buttonRef}
onClick={disableButton}
>
    Add
</button>

Similarly you can enable the button by using buttonRef.current.disabled = false

You shouldn't be setting the value of the input through refs.

Take a look at the documentation for controlled form components here - https://facebook.github.io/react/docs/forms.html#controlled-components

In a nutshell

<input value={this.state.value} onChange={(e) => this.setState({value: e.target.value})} />

Then you will be able to control the disabled state by using disabled={!this.state.value}

There are few typical methods how we control components render in React.

But, I haven't used any of these in here, I just used the ref's to namespace underlying children to the component.

class AddItem extends React.Component {_x000D_
    change(e) {_x000D_
      if ("" != e.target.value) {_x000D_
        this.button.disabled = false;_x000D_
      } else {_x000D_
        this.button.disabled = true;_x000D_
      }_x000D_
    }_x000D_
_x000D_
    add(e) {_x000D_
      console.log(this.input.value);_x000D_
      this.input.value = '';_x000D_
      this.button.disabled = true;_x000D_
    }_x000D_
_x000D_
    render() {_x000D_
        return (_x000D_
          <div className="add-item">_x000D_
          <input type="text" className = "add-item__input" ref = {(input) => this.input=input} onChange = {this.change.bind(this)} />_x000D_
          _x000D_
          <button className="add-item__button" _x000D_
          onClick= {this.add.bind(this)} _x000D_
          ref={(button) => this.button=button}>Add_x000D_
          </button>_x000D_
          </div>_x000D_
        );_x000D_
    }_x000D_
}_x000D_
_x000D_
ReactDOM.render(<AddItem / > , document.getElementById('root'));

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>_x000D_
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>_x000D_
<div id="root"></div>