React js onClick can't pass value to method

Question

I want to read the onClick event value properties. But when I click on it, I see something like this on the console:

SyntheticMouseEvent {dispatchConfig: Ob         


        

Answer 1

You can simply do it if you are using ES6.

export default class Container extends Component {
  state = {
    data: [
        // ...
    ]
  }

  handleItemChange = (e, data) => {
      // here the data is available 
      // ....
  }
  render () {
     return (
        <div>
        {
           this.state.data.map((item, index) => (
              <div key={index}>
                  <Input onChange={(event) => this.handItemChange(event, 
                         item)} value={item.value}/>
              </div>
           ))
        }
        </div>
     );
   }
 }

Answer 2

Easy Way

Use an arrow function:

return (
  <th value={column} onClick={() => this.handleSort(column)}>{column}</th>
);

This will create a new function that calls handleSort with the right params.

Better Way

Extract it into a sub-component. The problem with using an arrow function in the render call is it will create a new function every time, which ends up causing unneeded re-renders.

If you create a sub-component, you can pass handler and use props as the arguments, which will then re-render only when the props change (because the handler reference now never changes):

Sub-component

class TableHeader extends Component {
  handleClick = () => {
    this.props.onHeaderClick(this.props.value);
  }

  render() {
    return (
      <th onClick={this.handleClick}>
        {this.props.column}
      </th>
    );
  }
}

Main component

{this.props.defaultColumns.map((column) => (
  <TableHeader
    value={column}
    onHeaderClick={this.handleSort}
  />
))}

---

Old Easy Way (ES5)

Use .bind to pass the parameter you want, this way you are binding the function with the Component context :

return (
  <th value={column} onClick={this.handleSort.bind(this, column)}>{column}</th>
);

Answer 3

Using arrow function :

You must install stage-2:

npm install babel-preset-stage-2 :

class App extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            value=0
        }
    }

    changeValue = (data) => (e) => {
        alert(data);  //10
        this.setState({ [value]: data })
    }

    render() {
        const data = 10;
        return (
            <div>
                <input type="button" onClick={this.changeValue(data)} />
            </div>
        );
    }
}
export default App; 

Answer 4

1. You just have to use an arrow function in the Onclick event like this: 

<th value={column} onClick={() => that.handleSort(theValue)} >{column}</th>

2.Then bind this in the constructor method:
    this.handleSort = this.handleSort.bind(this);

3.And finally get the value in the function:
  handleSort(theValue){
     console.log(theValue);
}

Answer 5

Theres' a very easy way.

 onClick={this.toggleStart('xyz')} . 
  toggleStart= (data) => (e) =>{
     console.log('value is'+data);  
 }

Answer 6

I wrote a wrapper component that can be reused for this purpose that builds on the accepted answers here. If all you need to do is pass a string however, then just add a data-attribute and read it from e.target.dataset (like some others have suggested). By default my wrapper will bind to any prop that is a function and starts with 'on' and automatically pass the data prop back to the caller after all the other event arguments. Although I haven't tested it for performance, it will give you the opportunity to avoid creating the class yourself, and it can be used like this:

const DataButton = withData('button')
const DataInput = withData('input');

or for Components and functions

const DataInput = withData(SomeComponent);

or if you prefer

const DataButton = withData(<button/>)

declare that Outside your container (near your imports)

Here is usage in a container:

import withData from './withData';
const DataInput = withData('input');

export default class Container extends Component {
    state = {
         data: [
             // ...
         ]
    }

    handleItemChange = (e, data) => {
        // here the data is available 
        // ....
    }

    render () {
        return (
            <div>
                {
                    this.state.data.map((item, index) => (
                        <div key={index}>
                            <DataInput data={item} onChange={this.handleItemChange} value={item.value}/>
                        </div>
                    ))
                }
            </div>
        );
    }
}

Here is the wrapper code 'withData.js:

import React, { Component } from 'react';

const defaultOptions = {
    events: undefined,
}

export default (Target, options) => {
    Target = React.isValidElement(Target) ? Target.type : Target;
    options = { ...defaultOptions, ...options }

    class WithData extends Component {
        constructor(props, context){
            super(props, context);
            this.handlers = getHandlers(options.events, this);        
        }

        render() {
            const { data, children, ...props } = this.props;
            return <Target {...props} {...this.handlers} >{children}</Target>;
        }

        static displayName = `withData(${Target.displayName || Target.name || 'Component'})`
    }

    return WithData;
}

function getHandlers(events, thisContext) {
    if(!events)
        events = Object.keys(thisContext.props).filter(prop => prop.startsWith('on') && typeof thisContext.props[prop] === 'function')
    else if (typeof events === 'string')
        events = [events];

    return events.reduce((result, eventType) => {
        result[eventType] = (...args) => thisContext.props[eventType](...args, thisContext.props.data);
        return result;
    }, {});
}