[javascript] React JS onClick event handler

I have

var TestApp = React.createClass({
      getComponent: function(){
          console.log(this.props);
      },
      render: function(){
        return(
             <div>
             <ul>
                <li onClick={this.getComponent}>Component 1</li>
             </ul>
             </div>
        );
      }
});
React.renderComponent(<TestApp />, document.body);

I want to color the background of the clicked list element. How can I do this in React ?

Something like

$('li').on('click', function(){
    $(this).css({'background-color': '#ccc'});
});

class FrontendSkillList extends React.Component {_x000D_
  constructor() {_x000D_
    super();_x000D_
    this.state = { selectedSkill: {} };_x000D_
  }_x000D_
  render() {_x000D_
    return (_x000D_
      <ul>_x000D_
        {this.props.skills.map((skill, i) => (_x000D_
            <li_x000D_
              className={_x000D_
                this.state.selectedSkill.id === skill.id ? "selected" : ""_x000D_
              }_x000D_
              onClick={this.selectSkill.bind(this, skill)}_x000D_
              style={{ cursor: "pointer" }}_x000D_
              key={skill.id}_x000D_
            >_x000D_
            {skill.name}_x000D_
            </li>_x000D_
        ))}_x000D_
      </ul>_x000D_
    );_x000D_
  }_x000D_
_x000D_
  selectSkill(selected) {_x000D_
    if (selected.id !== this.state.selectedSkill.id) {_x000D_
      this.setState({ selectedSkill: selected });_x000D_
    } else {_x000D_
      this.setState({ selectedSkill: {} });_x000D_
    }_x000D_
  }_x000D_
}_x000D_
_x000D_
const data = [_x000D_
  { id: "1", name: "HTML5" },_x000D_
  { id: "2", name: "CSS3" },_x000D_
  { id: "3", name: "ES6 & ES7" }_x000D_
];_x000D_
const element = (_x000D_
  <div>_x000D_
    <h1>Frontend Skill List</h1>_x000D_
    <FrontendSkillList skills={data} />_x000D_
  </div>_x000D_
);_x000D_
ReactDOM.render(element, document.getElementById("root"));

.selected {_x000D_
  background-color: rgba(217, 83, 79, 0.8);_x000D_
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>_x000D_
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>_x000D_
_x000D_
<div id="root"></div>

@user544079 Hope this demo can help :) I recommend changing background color by toggling classname.

Two ways I can think of are

var TestApp = React.createClass({
    getComponent: function(index) {
        $(this.getDOMNode()).find('li:nth-child(' + index + ')').css({
            'background-color': '#ccc'
        });
    },
    render: function() {
        return (
            <div>
              <ul>
                <li onClick={this.getComponent.bind(this, 1)}>Component 1</li>
                <li onClick={this.getComponent.bind(this, 2)}>Component 2</li>
                <li onClick={this.getComponent.bind(this, 3)}>Component 3</li>
              </ul>
            </div>
        );
    }
});
React.renderComponent(<TestApp /> , document.getElementById('soln1'));

This is my personal favorite.

var ListItem = React.createClass({
    getInitialState: function() {
        return {
            isSelected: false
        };
    },
    handleClick: function() {
        this.setState({
            isSelected: true
        })
    },
    render: function() {
        var isSelected = this.state.isSelected;
        var style = {
            'background-color': ''
        };
        if (isSelected) {
            style = {
                'background-color': '#ccc'
            };
        }
        return (
            <li onClick={this.handleClick} style={style}>{this.props.content}</li>
        );
    }
});

var TestApp2 = React.createClass({
    getComponent: function(index) {
        $(this.getDOMNode()).find('li:nth-child(' + index + ')').css({
            'background-color': '#ccc'
        });
    },
    render: function() {
        return (
            <div>
             <ul>
              <ListItem content="Component 1" />
              <ListItem content="Component 2" />
              <ListItem content="Component 3" />
             </ul>
            </div>
        );
    }
});
React.renderComponent(<TestApp2 /> , document.getElementById('soln2'));

Here is a DEMO

I hope this helps.

Why not:

onItemClick: function (event) {

    event.currentTarget.style.backgroundColor = '#ccc';

},

render: function() {
    return (
        <div>
            <ul>
                <li onClick={this.onItemClick}>Component 1</li>
            </ul>
        </div>
    );
}

And if you want to be more React-ive about it, you might want to set the selected item as state of its containing React component, then reference that state to determine the item's color within render:

onItemClick: function (event) {

    this.setState({ selectedItem: event.currentTarget.dataset.id });
    //where 'id' =  whatever suffix you give the data-* li attribute
},

render: function() {
    return (
        <div>
            <ul>
                <li onClick={this.onItemClick} data-id="1" className={this.state.selectedItem == 1 ? "on" : "off"}>Component 1</li>
                <li onClick={this.onItemClick} data-id="2" className={this.state.selectedItem == 2 ? "on" : "off"}>Component 2</li>
                <li onClick={this.onItemClick} data-id="3" className={this.state.selectedItem == 3 ? "on" : "off"}>Component 3</li>
            </ul>
        </div>
    );
},

You'd want to put those <li>s into a loop, and you need to make the li.on and li.off styles set your background-color.

Handling events with React elements is very similar to handling events on DOM elements. There are some syntactic differences:

• React events are named using camelCase, rather than lowercase.
• With JSX you pass a function as the event handler, rather than a string.

So as mentioned in React documentation, they quite similar to normal HTML when it comes to Event Handling, but event names in React using camelcase, because they are not really HTML, they are JavaScript, also, you pass the function while we passing function call in a string format for HTML, they are different, but the concepts are pretty similar...

Look at the example below, pay attention to the way event get passed to the function:

function ActionLink() {
  function handleClick(e) {
    e.preventDefault();
    console.log('The link was clicked.');
  }

  return (
    <a href="#" onClick={handleClick}>
      Click me
    </a>
  );
}

If you're using ES6, here's some simple example code:

import React from 'wherever_react_is';

class TestApp extends React.Component {

  getComponent(event) {
      console.log('li item clicked!');
      event.currentTarget.style.backgroundColor = '#ccc';
  }

  render() {
    return(
       <div>
         <ul>
            <li onClick={this.getComponent.bind(this)}>Component 1</li>
         </ul>
       </div>
    );
  }
}

export default TestApp;

In ES6 class bodies, functions no longer require the 'function' keyword and they don't need to be separated by commas. You can also use the => syntax as well if you wish.

Here's an example with dynamically created elements:

import React from 'wherever_react_is';

class TestApp extends React.Component {

constructor(props) {
  super(props);

  this.state = {
    data: [
      {name: 'Name 1', id: 123},
      {name: 'Name 2', id: 456}
    ]
  }
}

  getComponent(event) {
      console.log('li item clicked!');
      event.currentTarget.style.backgroundColor = '#ccc';
  }

  render() {        
       <div>
         <ul>
         {this.state.data.map(d => {
           return(
              <li key={d.id} onClick={this.getComponent.bind(this)}>{d.name}</li>
           )}
         )}
         </ul>
       </div>
    );
  }
}

export default TestApp;

Note that each dynamically created element should have a unique reference 'key'.

Furthermore, if you would like to pass the actual data object (rather than the event) into your onClick function, you will need to pass that into your bind. For example:

New onClick function:

getComponent(object) {
    console.log(object.name);
}

Passing in the data object:

{this.state.data.map(d => {
    return(
      <li key={d.id} onClick={this.getComponent.bind(this, d)}>{d.name}</li>
    )}
)}

This is a non-standard (but not so uncommon) React pattern that doesn't use JSX, instead putting everything inline. Also, it's Coffeescript.

The 'React-way' to do this would be with the component's own state:

(c = console.log.bind console)

mock_items: [
    {
        name: 'item_a'
        uid: shortid()
    }
    {
        name: 'item_b'
        uid: shortid()
    }
    {
        name: 'item_c'
        uid: shortid()
    }
]
getInitialState: ->
    lighted_item: null
render: ->
    div null,
        ul null,
            for item, idx in @mock_items
                uid = item.uid
                li
                    key: uid
                    onClick: do (idx, uid) =>
                        (e) =>
                            # justf to illustrate these are bound in closure by the do lambda,
                            c idx
                            c uid
                            @setState
                                lighted_item: uid
                    style:
                        cursor: 'pointer'
                        background: do (uid) =>
                            c @state.lighted_item
                            c 'and uid', uid
                            if @state.lighted_item is uid then 'magenta' else 'chartreuse'
                        # background: 'chartreuse'
                    item.name

This example works -- I tested it locally. You can check out this example code exactly at my github. Originally the env was only local for my own whiteboard r&d purposes but I posted it to Github for this. It may get written over at some point but you can check out the commit from Sept 8, 2016 to see this.

More generally, if you want to see how this CS/no-JSX pattern for React works, check out some recent work here. It's possible I will have time to fully implement a POC for this app idea, the stack for which includes NodeJS, Primus, Redis, & React.

Use ECMA2015. Arrow functions make "this" a lot more intuitive.

import React from 'react';


class TestApp extends React.Component {
   getComponent(e, index) {
       $(e.target).css({
           'background-color': '#ccc'
       });
   }
   render() {
       return (
           <div>
             <ul>
               <li onClick={(e) => this.getComponent(e, 1)}>Component 1</li>
               <li onClick={(e) => this.getComponent(e, 2)}>Component 2</li>
               <li onClick={(e) => this.getComponent(e, 3)}>Component 3</li>
             </ul>
           </div>
       );
   }
});
React.renderComponent(<TestApp /> , document.getElementById('soln1'));`

You can make use of the React.createClone method. Create your element, than create a clone of it. During the clone's creation, you can inject props. Inject an onClick : method prop like this

{ onClick : () => this.changeColor(originalElement, index) }

the changeColor method will set the state with the duplicate, allowing you sto set the color in the process.

render()_x000D_
  {_x000D_
    return(_x000D_
      <ul>_x000D_
_x000D_
        {this.state.items.map((val, ind) => {_x000D_
          let item = <li key={ind}>{val}</li>;_x000D_
          let props = { _x000D_
            onClick: () => this.Click(item, ind),_x000D_
            key : ind,_x000D_
            ind_x000D_
          }_x000D_
          let clone = React.cloneElement(item, props, [val]);_x000D_
          return clone;_x000D_
        })}_x000D_
_x000D_
      </ul>_x000D_
    )_x000D_
  }

Here is how you define a react onClick event handler, which was answering the question title... using es6 syntax

import React, { Component } from 'react';

export default class Test extends Component {
  handleClick(e) {
    e.preventDefault()
    console.log(e.target)
  }

  render() {
    return (
      <a href='#' onClick={e => this.handleClick(e)}>click me</a>
    )
  }
}