CODEWITHSUNDEEP
javascriptreactjs
user544079
user544079

Reputation: 16639

OnChange event using React JS for drop down

var MySelect = React.createClass({
     change: function(){
         return document.querySelector('#lang').value;
     },
     render: function(){
        return(
           <div>
               <select id="lang">
                  <option value="select" onChange={this.change}>Select</option>
                  <option value="Java" onChange={this.change}>Java</option>
                  <option value="C++" onChange={this.change}>C++</option>
               </select>
               <p></p>
               <p value={this.change}></p>
           </div>
        );
     }
});

React.render(<MySelect />, document.body);

The onChange event does not work.

Upvotes: 279

Views: 852341

Answers (10)

Felix Kling
Felix Kling

Reputation: 817030

The change event is triggered on the <select> element, not the <option> element. However, that's not the only problem. The way you defined the change function won't cause a rerender of the component. It seems like you might not have fully grasped the concept of React yet, so maybe "Thinking in React" helps.

You have to store the selected value as state and update the state when the value changes. Updating the state will trigger a rerender of the component.

var MySelect = React.createClass({
     getInitialState: function() {
         return {
             value: 'select'
         }
     },
     change: function(event){
         this.setState({value: event.target.value});
     },
     render: function(){
        return(
           <div>
               <select id="lang" onChange={this.change} value={this.state.value}>
                  <option value="select">Select</option>
                  <option value="Java">Java</option>
                  <option value="C++">C++</option>
               </select>
               <p></p>
               <p>{this.state.value}</p>
           </div>
        );
     }
});

React.render(<MySelect />, document.body);

Also note that <p> elements don't have a value attribute. React/JSX simply replicates the well-known HTML syntax, it doesn't introduce custom attributes (with the exception of key and ref). If you want the selected value to be the content of the <p> element then simply put inside of it, like you would do with any static content.

Learn more about event handling, state and form controls:

Upvotes: 450

Austin Gayler
Austin Gayler

Reputation: 4376

Hooks and TypeScript, with the state living in the parent component:

import React from 'react';

interface Option {
  value: string;
  label: string;
}

interface DropdownProps {
  options: Option[];
  selectedOption: string;
  onOptionChange: (value: string) => void;
}

const Dropdown: React.FC<DropdownProps> = ({ options, selectedOption, onOptionChange }) => {
  return (
    <select
      value={selectedOption}
      onChange={(e) => onOptionChange(e.target.value)}
    >
      {options.map((o) => (
        <option key={o.value} value={o.value}>
          {o.label}
        </option>
      ))}
    </select>
  );
};

const Parent: React.FC = () => {
  const options: Option[] = [
    { value: 'option1', label: 'Option 1' },
    { value: 'option2', label: 'Option 2' },
    { value: 'option3', label: 'Option 3' },
  ];

  const [selectedOption, setSelectedOption] = useState<string>(options[0].value);

  const handleOptionChange = (value: string) => {
    setSelectedOption(value);
  };

  return (
    <div>
      <Dropdown options={options} selectedOption={selectedOption} onOptionChange={handleOptionChange} />
      <p>Your selected option: {selectedOption}</p>
    </div>
  );
};

Upvotes: 0

Krishnadas PC
Krishnadas PC

Reputation: 6539

Now you can use it like this

import { useState } from 'react';
import './App.css';

function App() {
  const [selectedItem, setSelectedItem] = useState("Counter")
  const handleChange = (e) => {
    setSelectedItem(e.target.value)
  }
  return (
    <div className="App">
      <p>You have selected {selectedItem}</p>
      <select name='item-selected' value={selectedItem} onChange={handleChange}>
        <option value="Counter">Counter</option>
        <option value="useEffect">useEffect</option>
      </select>
    </div>
  );
}

export default App;

Upvotes: 5

PWJ
PWJ

Reputation: 81

I'll add this here, in case it helps someone because this was the solution that helped me.

This is to get the SELECTED INDEX. Not for the value. (Worked for me because my options list was a list of numbers)

const [selectedOption, setSelectedOption] = useState(0)
<select onChange={event => setSelectedOption(event.target.options.selectedIndex)}>

Upvotes: 4

Pharis Kahama
Pharis Kahama

Reputation: 131

  handleChange(value, selectOptionSetter) => {
     selectOptionSetter(value)
     // handle other stuff like persisting to store etc
   }

  const Dropdown = (props) => {
  const { options } = props;
  const [selectedOption, setSelectedOption] = useState(options[0].value);
  return (
      <select
        value={selectedOption}
        onChange={e => handleChange(e.target.value, setSelectedOption)}>
        {options.map(o => (
          <option key={o.value} value={o.value}>{o.label}</option>
        ))}
      </select>
  );
};

Upvotes: 12

Austin Gayler
Austin Gayler

Reputation: 4376

React Hooks (16.8+):

const Dropdown = ({
  options
}) => {
  const [selectedOption, setSelectedOption] = useState(options[0].value);
  return (
      <select
        value={selectedOption}
        onChange={e => setSelectedOption(e.target.value)}>
        {options.map(o => (
          <option key={o.value} value={o.value}>{o.label}</option>
        ))}
      </select>
  );
};

Upvotes: 97

Sourav Purkait
Sourav Purkait

Reputation: 344

var MySelect = React.createClass({
getInitialState: function() {
 


var MySelect = React.createClass({
 getInitialState: function() {
     return {
         value: 'select'
     }
 },
 change: function(event){
     event.persist(); //THE MAIN LINE THAT WILL SET THE VALUE
     this.setState({value: event.target.value});
 },
 render: function(){
    return(
       <div>
           <select id="lang" onChange={this.change.bind(this)} value={this.state.value}>
              <option value="select">Select</option>
              <option value="Java">Java</option>
              <option value="C++">C++</option>
           </select>
           <p></p>
           <p>{this.state.value}</p>
       </div>
    );
 }
});
React.render(<MySelect />, document.body); 
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>

Upvotes: 0

Satish
Satish

Reputation: 1065

If you are using select as inline to other component, then you can also use like given below.

<select onChange={(val) => this.handlePeriodChange(val.target.value)} className="btn btn-sm btn-outline-secondary dropdown-toggle">
    <option value="TODAY">Today</option>
    <option value="THIS_WEEK" >This Week</option>
    <option value="THIS_MONTH">This Month</option>
    <option value="THIS_YEAR">This Year</option>
    <option selected value="LAST_AVAILABLE_DAY">Last Availabe NAV Day</option>
</select>

And on the component where select is used, define the function to handle onChange like below:

handlePeriodChange(selVal) {
    this.props.handlePeriodChange(selVal);
}

Upvotes: 4

Abolfazl Miadian
Abolfazl Miadian

Reputation: 3159

Thank you Felix Kling, but his answer need a little change:

var MySelect = React.createClass({
 getInitialState: function() {
     return {
         value: 'select'
     }
 },
 change: function(event){
     this.setState({value: event.target.value});
 },
 render: function(){
    return(
       <div>
           <select id="lang" onChange={this.change.bind(this)} value={this.state.value}>
              <option value="select">Select</option>
              <option value="Java">Java</option>
              <option value="C++">C++</option>
           </select>
           <p></p>
           <p>{this.state.value}</p>
       </div>
    );
 }
});
React.render(<MySelect />, document.body);

Upvotes: 1

Kirk Strobeck
Kirk Strobeck

Reputation: 18649

import React, { PureComponent, Fragment } from 'react';
import ReactDOM from 'react-dom';

class Select extends PureComponent {
  state = {
    options: [
      {
        name: 'Select…',
        value: null,
      },
      {
        name: 'A',
        value: 'a',
      },
      {
        name: 'B',
        value: 'b',
      },
      {
        name: 'C',
        value: 'c',
      },
    ],
    value: '?',
  };

  handleChange = (event) => {
    this.setState({ value: event.target.value });
  };

  render() {
    const { options, value } = this.state;

    return (
      <Fragment>
        <select onChange={this.handleChange} value={value}>
          {options.map(item => (
            <option key={item.value} value={item.value}>
              {item.name}
            </option>
          ))}
        </select>
        <h1>Favorite letter: {value}</h1>
      </Fragment>
    );
  }
}

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

Upvotes: 45

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