So I'm rendering components from an array 'values': ["hello", "world] successfully but I would like to add a button component so that every time it gets clicked, another empty field shows up. This is what it currently looks like:
but i would like it so that there is a button and every time I click on it, it renders another empty component to input text. Would it be correct to add a button component directly inside the my array_node.jsx file? Is what I'm doing correct so far? Would I also have to add some sort of newInput: function() in side the var AddButton = React.createClass({})? Thank you!
array_node.jsx:
{...
childChange: function(name, valid, value) {
// update state
this.state.values = this.props.values;
// Using regex to find last digits from 0-9
var pattern = /[0-9]/;
var match = name.match(pattern);
// Parse char into int
var i = parseInt(match);
this.state.values[i] = value;
this.setState(this.state);
// Call parent callback
this.props.callback(
this.props.name,
this.props.node.valid(this.state.values),
this.state.values
);
},
addItem: function(values){
},
render: function() {
var that = this;
return (
<div id = "form">
{this.props.values.map(function(v, i) {
return (
<div>
{(that.props.node.get().constructor.name === "Parent") ?
<ParentComponent
name={that.props.name + i}
key={i}
timer={that.props.timer}
callback={that.childChange}
values={v}
newParent={that.props.node.get()}
/>
:
<NodeComponent
name={that.props.name + i}
key={i}
timer={that.props.timer}
callback={that.childChange}
value={v}
newNode={that.props.node.get()}
/>
}
</div>
)
})}
</div>
)
}
});
return ArrayNodeComponent
var AddButton = React.createClass({
addItem: function() {
},
render: function() {
return(
<div id="create_new_entry">
</div>
)
}
})
formatoc:
var props = {
'name' : 'form',
'timer' : 1500,
'callback' : function(id, validity, value) {console.log(id, validity, value);},
'values': ["hello", "world"],
'node' : new FormatOC.ArrayNode({"__array__":"unique", "__type__":"string","__minimum__":1,"__maximum__":200,"__component__":"Input"},
)
}
React.render(React.createElement(ArrayNodeComponent, props), document.getElementById('react-component'));
You might add a button into your form within the render function.
Then listen to clicks and add a new empty element to your values list.
if you would like to propagate the changes to some parent component, you would have to pass the onClick handler from the parent component and update the values list there too.
import { Component } from 'react';
class ArrayNodeComponent extends Component {
// other code ...
// like your initialisation of your state
// and other functions
addEmptyItem() {
const { values } = this.state;
this.setState({
values: [...values, ""]
});
}
render() {
return (
<form id="test">
{
/* this is your values map routine, shortened */
this.props.values.map(function(v, i) { /*...*/ })
}
<button onClick={() => this.addEmptyItem()}>Add</button>
</form>
);
}
}
Btw in this simple scenario, it would not make sense to create a custom Button component.
I have a list with around 2k items. If I use onClick on each child, I would end up with 2k listeners which is what I have currently. I would want to do something like making the parent component listen to the click events instead. But if I do that, I don't have reference to the child component which I need to call setState on. Also the list of child components can be filtered dynamically (using this.refs might be bad ?).
The best I can come up with is to make a hash of child components id mapping to child components in the parent and look up the view on click.
Just for illustration purposes:
var Parent = React.createClass({
shouldComponentUpdate: function() { return false; },
handler: function(e) {
// look up from reference and set state
},
componentWillUnmount: function() {
// clean up reference
},
render: function() {
this.reference = {};
var items = [];
for(var i = 0; i < this.props.items.length; i++) {
var child = React.createClass(Child, {id: this.props.items[i].id});
items.push(child);
reference[child.id] = child;
}
return React.createClass('div', {onClick: this.handler}, items);
}
})
I wonder if there is a React way of dealing with this.
I think this answer may help... It does not matter if you have 2000 event handlers or just one. React deals with it in the same way. Remember that the HTML you return in your render method does not get added to the DOM but it is just used by React to build a virtual DOM representation. In the end, React has only one onClick.
React efficient way to bind event to many dom elements
If you need to know what element triggered the click you just need to access event.target and use any data-attribute to identify the clicked element.
The React way of doing this would be to use a Flux dispatcher + a Store. Basically, you can have each item bind to an event that gets triggered from the store once the store has carried out the tasks you want it to complete.
So the flow will be:
Item gets clicked => Flux event is dispatched => Flux dispatcher hears the events and executes the appropriate function with the data passed from Item component.
var ItemStore = {
doSomething: function(data){
// do something with the data
}
}
MicroEvent.mixin(ItemStore);
var AppDispatcher = new Dispatcher();
AppDispatcher.register(function(payload) {
switch (payload.eventName) {
case 'item-clicked':
ItemStore.doSomething(payload.data.someData);
ItemStore.trigger('did-something');
}
return true;
})
var Item = React.createClass({
shouldComponentUpdate: function() { return false; },
componentDidMount: function() {
ItemStore.bind('did-something', this.submitHandled);
},
handler: function(e) {
AppDispatcher.dispatch({
eventName: 'item-clicked',
data: {
someData: 'sample data'
}
});
},
componentWillUnmount: function() {
// clean up reference
},
submitHandled: function() {
// do something after the click
},
render: function() {
// insert your item's html here.
}
})
Building on #damianmr's answer, here's an example.
var Child = React.createClass({
shouldComponentUpdate(nextProps){
if (this.props.text !== nextProps.text) return true;
if (this.props.active !== nextProps.active) return true;
return false;
},
render(){
var className = 'Child';
if (this.props.active) className += ' Child-active';
return (
<div {...this.props} className={className}>
{this.props.text}
</div>
);
}
});
var Parent = React.createClass({
getInitialState(){
return {active: -1};
},
setActive(id){
this.setState({active: id});
},
render(){
return (
<div>
{this.props.items.map((item) => {
return (
<Child
active={this.state.active === item.id}
onClick={() => this.setActive(item.id)}
text={'My id is ' + item.id}
key={item.id}
/>
);
})}
</div>
);
}
});
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: Object, dispatchMarker: ".1.1.0.2.0.0:1", nativeEvent: MouseEvent, type: "click", target
My code is working correctly. When I run I can see {column} but can't get it in the onClick event.
My Code:
var HeaderRows = React.createClass({
handleSort: function(value) {
console.log(value);
},
render: function () {
var that = this;
return(
<tr>
{this.props.defaultColumns.map(function (column) {
return (
<th value={column} onClick={that.handleSort} >{column}</th>
);
})}
{this.props.externalColumns.map(function (column) {
// Multi dimension array - 0 is column name
var externalColumnName = column[0];
return ( <th>{externalColumnName}</th>);
})}
</tr>
);
}
});
How can I pass a value to the onClick event in React js?
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>
);
There are nice answers here, and i agree with #Austin Greco (the second option with separate components)
There is another way i like, currying.
What you can do is create a function that accept a parameter (your parameter) and returns another function that accepts another parameter (the click event in this case). then you are free to do with it what ever you want.
ES5:
handleChange(param) { // param is the argument you passed to the function
return function (e) { // e is the event object that returned
};
}
ES6:
handleChange = param => e => {
// param is the argument you passed to the function
// e is the event object that returned
};
And you will use it this way:
<input
type="text"
onChange={this.handleChange(someParam)}
/>
Here is a full example of such usage:
const someArr = ["A", "B", "C", "D"];
class App extends React.Component {
state = {
valueA: "",
valueB: "some initial value",
valueC: "",
valueD: "blah blah"
};
handleChange = param => e => {
const nextValue = e.target.value;
this.setState({ ["value" + param]: nextValue });
};
render() {
return (
<div>
{someArr.map(obj => {
return (
<div>
<label>
{`input ${obj} `}
</label>
<input
type="text"
value={this.state["value" + obj]}
onChange={this.handleChange(obj)}
/>
<br />
<br />
</div>
);
})}
</div>
);
}
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
<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="root"></div>
Note that this approach doesn't solve the creation of a new instance on each render.
I like this approach over the other inline handlers as this one is more concise and readable in my opinion.
Edit:
As suggested in the comments below, you can cache / memoize the result of the function.
Here is a naive implementation:
let memo = {};
const someArr = ["A", "B", "C", "D"];
class App extends React.Component {
state = {
valueA: "",
valueB: "some initial value",
valueC: "",
valueD: "blah blah"
};
handleChange = param => {
const handler = e => {
const nextValue = e.target.value;
this.setState({ ["value" + param]: nextValue });
}
if (!memo[param]) {
memo[param] = e => handler(e)
}
return memo[param]
};
render() {
return (
<div>
{someArr.map(obj => {
return (
<div key={obj}>
<label>
{`input ${obj} `}
</label>
<input
type="text"
value={this.state["value" + obj]}
onChange={this.handleChange(obj)}
/>
<br />
<br />
</div>
);
})}
</div>
);
}
}
const rootElement = document.getElementById("root");
ReactDOM.render(<App />, rootElement);
<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="root" />
Nowadays, with ES6, I feel we could use an updated answer.
return (
<th value={column} onClick={()=>this.handleSort(column)} >{column}</th>
);
Basically, (for any that don't know) since onClick is expecting a function passed to it, bind works because it creates a copy of a function. Instead we can pass an arrow function expression that simply invokes the function we want, and preserves this. You should never need to bind the render method in React, but if for some reason you're losing this in one of your component methods:
constructor(props) {
super(props);
this.myMethod = this.myMethod.bind(this);
}
[[h/t to #E.Sundin for linking this in a comment]
The top answer (anonymous functions or binding) will work, but it's not the most performant, as it creates a copy of the event handler for every instance generated by the map() function.
This is an explanation of the optimal way to do it from the ESLint-plugin-react:
Lists of Items
A common use case of bind in render is when rendering a list, to have
a separate callback per list item:
const List = props => (
<ul>
{props.items.map(item =>
<li key={item.id} onClick={() => console.log(item.id)}>
...
</li>
)}
</ul>
);
Rather than doing it this way, pull the repeated section into its own
component:
const List = props => (
<ul>
{props.items.map(item =>
<ListItem
key={item.id}
item={item}
onItemClick={props.onItemClick} // assume this is passed down to List
/>
)}
</ul>
);
const ListItem = props => {
const _onClick = () => {
console.log(props.item.id);
}
return (
<li onClick={_onClick}>
...
</li>
);
});
This will speed up rendering, as it avoids the need to create new
functions (through bind calls) on every render.
This is my approach, not sure how bad it is, please comment
In the clickable element
return (
<th value={column} onClick={that.handleSort} data-column={column}> {column}</th>
);
and then
handleSort(e){
this.sortOn(e.currentTarget.getAttribute('data-column'));
}
React Hooks Solution 2022
const arr = [
{ id: 1, txt: 'One' },
{ id: 2, txt: 'Two' },
{ id: 3, txt: 'Three' },
]
const App = () => {
const handleClick = useCallback(
(id) => () => {
console.log("ID: ", id)
},
[],
)
return (
<div>
{arr.map((item) => (
<button onClick={handleClick(item.id)}>{item.txt}</button>
))}
</div>
)
}
You can pass a function to useCallback's return, you can then call your function normally in the render by passing params to it. Works like a charm! Just make sure you set your useCallback's dependency array appropriately.
Best Solution with React >= 16
The cleanest way I've found to call functions with multiple parameters in onClick, onChange etc. without using inline functions is to use the custom data attribute available in React 16 and above versions.
const App = () => {
const onClick = (e) => {
const value1 = e.currentTarget.getAttribute("data-value1")
const value2 = e.currentTarget.getAttribute("data-value2")
const value2 = e.currentTarget.getAttribute("data-value2")
console.log("Values1", value1)
console.log("Values2", value2)
console.log("Values3", value3)
}
return (
<button onClick={onClick} data-value1="a" data-value2="b" data-value3="c" />
)
}
Above example is for a functional component but the implementation is pretty similar even in class components.
This approach doesn't yield unnecessary re-renders because you aren't using inline functions, and you avoid the hassle of binding with this.
It allows you to pass as many values as you would like to use in your function.
If you are passing values as props to your children to be used in the Child Component's onClick, you can use this approach there as well, without creating a wrapper function.
Works with array of objects as well, in cases where you want to pass the id from the object to the onClick, as shown below.
const App = () => {
const [arrState, setArrState] = useState(arr)
const deleteContent = (e) => {
const id = e.currentTarget.getAttribute("data-id")
const tempArr = [...arrState]
const filteredArr = tempArr.filter((item) => item.id !== id)
setArrState(filteredArr)
}
return (
<div>
{arrState.map((item) => (
<React.Fragment key={item.id}>
<p>{item.content}</p>
<button onClick={deleteContent} data-id={item.id}>
Delete
</button>
</React.Fragment>
))}
</div>
)
}
this example might be little different from yours. but i can assure you that this is the best solution you can have for this problem.
i have searched for days for a solution which has no performance issue. and finally came up with this one.
class HtmlComponent extends React.Component {
constructor() {
super();
this.state={
name:'MrRehman',
};
this.handleClick= this.handleClick.bind(this);
}
handleClick(event) {
const { param } = e.target.dataset;
console.log(param);
//do what you want to do with the parameter
}
render() {
return (
<div>
<h3 data-param="value what you wanted to pass" onClick={this.handleClick}>
{this.state.name}
</h3>
</div>
);
}
}
UPDATE
incase you want to deal with objects that are supposed to be the parameters. you can use JSON.stringify(object) to convert to it to string and add to the data set.
return (
<div>
<h3 data-param={JSON.stringify({name:'me'})} onClick={this.handleClick}>
{this.state.name}
</h3>
</div>
);
Simply create a function like this
function methodName(params) {
//the thing you wanna do
}
and call it in the place you need
<Icon onClick = {() => { methodName(theParamsYouwantToPass);} }/>
class extends React.Component {
onClickDiv = (column) => {
// do stuff
}
render() {
return <div onClick={() => this.onClickDiv('123')} />
}
}
I realize this is pretty late to the party, but I think a much simpler solution could satisfy many use cases:
handleEdit(event) {
let value = event.target.value;
}
...
<button
value={post.id}
onClick={this.handleEdit} >Edit</button>
I presume you could also use a data- attribute.
Simple, semantic.
Making alternate attempt to answer OP's question including e.preventDefault() calls:
Rendered link (ES6)
<a href="#link" onClick={(e) => this.handleSort(e, 'myParam')}>
Component Function
handleSort = (e, param) => {
e.preventDefault();
console.log('Sorting by: ' + param)
}
One more option not involving .bind or ES6 is to use a child component with a handler to call the parent handler with the necessary props. Here's an example (and a link to working example is below):
var HeaderRows = React.createClass({
handleSort: function(value) {
console.log(value);
},
render: function () {
var that = this;
return(
<tr>
{this.props.defaultColumns.map(function (column) {
return (
<TableHeader value={column} onClick={that.handleSort} >
{column}
</TableHeader>
);
})}
{this.props.externalColumns.map(function (column) {
// Multi dimension array - 0 is column name
var externalColumnName = column[0];
return ( <th>{externalColumnName}</th>
);
})}
</tr>);
)
}
});
// A child component to pass the props back to the parent handler
var TableHeader = React.createClass({
propTypes: {
value: React.PropTypes.string,
onClick: React.PropTypes.func
},
render: function () {
return (
<th value={this.props.value} onClick={this._handleClick}
{this.props.children}
</th>
)
},
_handleClick: function () {
if (this.props.onClick) {
this.props.onClick(this.props.value);
}
}
});
The basic idea is for the parent component to pass the onClick function to a child component. The child component calls the onClick function and can access any props passed to it (and the event), allowing you to use any event value or other props within the parent's onClick function.
Here's a CodePen demo showing this method in action.
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>
);
}
}
There are couple of ways to pass parameter in event handlers, some are following.
You can use an arrow function to wrap around an event handler and pass parameters:
<button onClick={() => this.handleClick(id)} />
above example is equivalent to calling .bind or you can explicitly call bind.
<button onClick={this.handleClick.bind(this, id)} />
Apart from these two approaches, you can also pass arguments to a function that is defined as a curry function.
handleClick = (id) => () => {
console.log("Hello, your ticket number is", id)
};
<button onClick={this.handleClick(id)} />
Implementing show total count from an object by passing count as a parameter from main to sub components as described below.
Here is MainComponent.js
import React, { Component } from "react";
import SubComp from "./subcomponent";
class App extends Component {
getTotalCount = (count) => {
this.setState({
total: this.state.total + count
})
};
state = {
total: 0
};
render() {
const someData = [
{ name: "one", count: 200 },
{ name: "two", count: 100 },
{ name: "three", count: 50 }
];
return (
<div className="App">
{someData.map((nameAndCount, i) => {
return (
<SubComp
getTotal={this.getTotalCount}
name={nameAndCount.name}
count={nameAndCount.count}
key={i}
/>
);
})}
<h1>Total Count: {this.state.total}</h1>
</div>
);
}
}
export default App;
And Here is SubComp.js
import React, { Component } from 'react';
export default class SubComp extends Component {
calculateTotal = () =>{
this.props.getTotal(this.props.count);
}
render() {
return (
<div>
<p onClick={this.calculateTotal}> Name: {this.props.name} || Count: {this.props.count}</p>
</div>
)
}
};
Try to implement above and you will get exact scenario that how pass parameters works in reactjs on any DOM method.
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;
}, {});
}
I have below 3 suggestion to this on JSX onClick Events -
Actually, we don't need to use .bind() or Arrow function in our code. You can simple use in your code.
You can also move onClick event from th(or ul) to tr(or li) to improve the performance. Basically you will have n number of "Event Listeners" for your n li element.
So finally code will look like this:
<ul onClick={this.onItemClick}>
{this.props.items.map(item =>
<li key={item.id} data-itemid={item.id}>
...
</li>
)}
</ul>
// And you can access item.id in onItemClick method as shown below:
onItemClick = (event) => {
console.log(e.target.getAttribute("item.id"));
}
I agree with the approach mention above for creating separate React Component for ListItem and List. This make code looks good however if you have 1000 of li then 1000 Event Listeners will be created. Please make sure you should not have much event listener.
import React from "react";
import ListItem from "./ListItem";
export default class List extends React.Component {
/**
* This List react component is generic component which take props as list of items and also provide onlick
* callback name handleItemClick
* #param {String} item - item object passed to caller
*/
handleItemClick = (item) => {
if (this.props.onItemClick) {
this.props.onItemClick(item);
}
}
/**
* render method will take list of items as a props and include ListItem component
* #returns {string} - return the list of items
*/
render() {
return (
<div>
{this.props.items.map(item =>
<ListItem key={item.id} item={item} onItemClick={this.handleItemClick}/>
)}
</div>
);
}
}
import React from "react";
export default class ListItem extends React.Component {
/**
* This List react component is generic component which take props as item and also provide onlick
* callback name handleItemClick
* #param {String} item - item object passed to caller
*/
handleItemClick = () => {
if (this.props.item && this.props.onItemClick) {
this.props.onItemClick(this.props.item);
}
}
/**
* render method will take item as a props and print in li
* #returns {string} - return the list of items
*/
render() {
return (
<li key={this.props.item.id} onClick={this.handleItemClick}>{this.props.item.text}</li>
);
}
}
I have added code for onclick event value pass to the method in two ways . 1 . using bind method 2. using arrow(=>) method . see the methods handlesort1 and handlesort
var HeaderRows = React.createClass({
getInitialState : function() {
return ({
defaultColumns : ["col1","col2","col2","col3","col4","col5" ],
externalColumns : ["ecol1","ecol2","ecol2","ecol3","ecol4","ecol5" ],
})
},
handleSort: function(column,that) {
console.log(column);
alert(""+JSON.stringify(column));
},
handleSort1: function(column) {
console.log(column);
alert(""+JSON.stringify(column));
},
render: function () {
var that = this;
return(
<div>
<div>Using bind method</div>
{this.state.defaultColumns.map(function (column) {
return (
<div value={column} style={{height : '40' }}onClick={that.handleSort.bind(that,column)} >{column}</div>
);
})}
<div>Using Arrow method</div>
{this.state.defaultColumns.map(function (column) {
return (
<div value={column} style={{height : 40}} onClick={() => that.handleSort1(column)} >{column}</div>
);
})}
{this.state.externalColumns.map(function (column) {
// Multi dimension array - 0 is column name
var externalColumnName = column;
return (<div><span>{externalColumnName}</span></div>
);
})}
</div>);
}
});
Below is the example which passes value on onClick event.
I used es6 syntax. remember in class component arrow function does not bind automatically, so explicitly binding in constructor.
class HeaderRows extends React.Component {
constructor(props) {
super(props);
this.handleSort = this.handleSort.bind(this);
}
handleSort(value) {
console.log(value);
}
render() {
return(
<tr>
{this.props.defaultColumns.map( (column, index) =>
<th value={ column }
key={ index }
onClick={ () => this.handleSort(event.target.value) }>
{ column }
</th>
)}
{this.props.externalColumns.map((column, index) =>
<th value ={ column[0] }
key={ index }>
{column[0]}
</th>
)}
</tr>
);
}
}
I guess you will have to bind the method to the React’s class instance. It’s safer to use a constructor to bind all methods in React. In your case when you pass the parameter to the method, the first parameter is used to bind the ‘this’ context of the method, thus you cannot access the value inside the method.
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);
}
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;
Theres' a very easy way.
onClick={this.toggleStart('xyz')} .
toggleStart= (data) => (e) =>{
console.log('value is'+data);
}
class TableHeader extends Component {
handleClick = (parameter,event) => {
console.log(parameter)
console.log(event)
}
render() {
return (
<button type="button"
onClick={this.handleClick.bind(this,"dataOne")}>Send</button>
);
}
}
Coming out of nowhere to this question, but i think .bind will do the trick. Find the sample code below.
const handleClick = (data) => {
console.log(data)
}
<button onClick={handleClick.bind(null, { title: 'mytitle', id: '12345' })}>Login</button>
There are 3 ways to handle this :-
Bind the method in constructor as :-
export class HeaderRows extends Component {
constructor() {
super();
this.handleSort = this.handleSort.bind(this);
}
}
Use the arrow function while creating it as :-
handleSort = () => {
// some text here
}
Third way is this :-
<th value={column} onClick={() => that.handleSort} >{column}</th>
You can use your code like this:
<th value={column} onClick={(e) => that.handleSort(e, column)} >{column}</th>
Here e is for event object, if you want to use event methods like preventDefault() in your handle function or want to get target value or name like e.target.name.
There were a lot of performance considerations, all in the vacuum.
The issue with this handlers is that you need to curry them in order to incorporate the argument that you can't name in the props.
This means that the component needs a handler for each and every clickable element. Let's agree that for a few buttons this is not an issue, right?
The problem arises when you are handling tabular data with dozens of columns and thousands of rows. There you notice the impact of creating that many handlers.
The fact is, I only need one.
I set the handler at the table level (or UL or OL...), and when the click happens I can tell which was the clicked cell using data available since ever in the event object:
nativeEvent.target.tagName
nativeEvent.target.parentElement.tagName
nativeEvent.target.parentElement.rowIndex
nativeEvent.target.cellIndex
nativeEvent.target.textContent
I use the tagname fields to check that the click happened in a valid element, for example ignore clicks in THs ot footers.
The rowIndex and cellIndex give the exact location of the clicked cell.
Textcontent is the text of the clicked cell.
This way I don't need to pass the cell's data to the handler, it can self-service it.
If I needed more data, data that is not to be displayed, I can use the dataset attribute, or hidden elements.
With some simple DOM navigation it's all at hand.
This has been used in HTML since ever, since PCs were much easier to bog.
When working with a function as opposed to a class, it's actually fairly easy.
const [breakfastMain, setBreakFastMain] = useState("Breakfast");
const changeBreakfastMain = (e) => {
setBreakFastMain(e.target.value);
//sometimes "value" won't do it, like for text, etc. In that case you need to
//write 'e.target/innerHTML'
}
<ul onClick={changeBreakfastMain}>
<li>
"some text here"
</li>
<li>
"some text here"
</li>
</ul>
I'd do it like this:
const HeaderRows = props => {
const handleSort = value => () => {
}
return <tr>
{props.defaultColumns.map((column, i) =>
<th key={i} onClick={handleSort(column)}>{column}</th>)}
{props.externalColumns.map((column, i) => {
// Multi dimension array - 0 is column name
const externalColumnName = column[0]
return (<th key={i}>{externalColumnName}</th>)
})}
</tr>
}
I was really disappointed by the performance I got on the following simple ReactJS example. When clicking on an item, the label (count) gets updated accordingly. Unfortunately, this takes roughly ~0.5-1 second to get updated. That's mainly due to "re-rendering" the entire todo list.
My understanding is that React's key design decision is to make the API seem like it re-renders the whole app on every update. It is supposed take the current state of the DOM and compare it with the target DOM representation, do a diff and update only the things that need to get updated.
Am I doing something which is not optimal? I could always update the count label manually (and the state silently) and that will be an almost instant operation but that takes away the point of using ReactJS.
/** #jsx React.DOM */
TodoItem = React.createClass({
getDefaultProps: function () {
return {
completedCallback: function () {
console.log('not callback provided');
}
};
},
getInitialState: function () {
return this.props;
},
updateCompletedState: function () {
var isCompleted = !this.state.data.completed;
this.setState(_.extend(this.state.data, {
completed: isCompleted
}));
this.props.completedCallback(isCompleted);
},
render: function () {
var renderContext = this.state.data ?
(<li className={'todo-item' + (this.state.data.completed ? ' ' + 'strike-through' : '')}>
<input onClick={this.updateCompletedState} type="checkbox" checked={this.state.data.completed ? 'checked' : ''} />
<span onClick={this.updateCompletedState} className="description">{this.state.data.description}</span>
</li>) : null;
return renderContext;
}
});
var TodoList = React.createClass({
getInitialState: function () {
return {
todoItems: this.props.data.todoItems,
completedTodoItemsCount: 0
};
},
updateCount: function (isCompleted) {
this.setState(_.extend(this.state, {
completedTodoItemsCount: isCompleted ? this.state.completedTodoItemsCount + 1 : this.state.completedTodoItemsCount - 1
}));
},
render: function () {
var updateCount = this.updateCount;
return (
<div>
<div>count: {this.state.completedTodoItemsCount}</div>
<ul className="todo-list">
{ this.state.todoItems.map(function (todoItem) {
return <TodoItem data={ todoItem } completedCallback={ updateCount } />
}) }
</ul>
</div>
);
}
});
var data = {todoItems: []}, i = 0;
while(i++ < 1000) {
data.todoItems.push({description: 'Comment ' + i, completed: false});
}
React.renderComponent(<TodoList data={ data } />, document.body);
<script src="http://fb.me/react-js-fiddle-integration.js"></script>
jsFiddle link, just in case: http://jsfiddle.net/9nrnz1qm/3/
If you do the following, you can cut the time down by a lot. It spends 25ms to 45ms to update for me.
use the production build
implement shouldComponentUpdate
update the state immutably
updateCompletedState: function (event) {
var isCompleted = event.target.checked;
this.setState({data:
_.extend({}, this.state.data, {
completed: isCompleted
})
});
this.props.completedCallback(isCompleted);
},
shouldComponentUpdate: function(nextProps, nextState){
return nextState.data.completed !== this.state.data.completed;
},
Updated fiddle
(there are a lot of questionable things about this code, daniula points out some of them)
When you are generating list of elements you should provide unique key prop for everyone. In your case:
<ul className="todo-list">
{ this.state.todoItems.map(function (todoItem, i) {
return <TodoItem key={i} data={ todoItem } completedCallback={ updateCount } />
}) }
</ul>
You can find out about this mistake by warning message in browser console:
Each child in an array should have a unique "key" prop. Check the render method of TodoList. See fb.me/react-warning-keys for more information.
There is another warning which you can easily fix by changing event handler on <input type="checkbox" /> inside <TodoItem /> from onClick to onChange:
<input onClick={this.updateCompletedState} type="checkbox" checked={this.state.data.completed ? 'checked' : ''} />
You are doing some string concatenation to set proper className. For more readable code try using nice and simple React.addons.classSet:
render: function () {
var renderContext = this.state.data ?
var cx = React.addons.classSet({
'todo-item': true,
'strike-through': this.state.data.completed
});
(<li className={ cx }>
<input onChange={this.updateCompletedState} type="checkbox" checked={this.state.data.completed ? 'checked' : ''} />
<span onClick={this.updateCompletedState} className="description">{this.state.data.description}</span>
</li>) : null;
return renderContext;
}
I'm looking at where you render() the list...
<div>
<div>count: {this.state.completedTodoItemsCount}</div>
<ul className="todo-list">
{ this.state.todoItems.map(function (todoItem) {
return <TodoItem data={ todoItem } completedCallback={ updateCount } />
}) }
</ul>
</div>
This should not be called every time a TodoItem is updated. Give the above element a surrounding div and an id like this:
return <div id={someindex++}><TodoItem
data={ todoItem }
completedCallback={ updateCount }
/></div>
Then simply rerender a single TodoItem as it is changed, like so:
ReactDOM.render(<TodoItem ...>, document.getElementById('someindex'));
ReactJS is supposed to be fast, yes, but you still need to stick to general programming paradigms, i.e., asking the machine to do as little as possible, thereby producing the result as fast as possible. Rerendering stuff that doesn't need to get re-rendered gets in the way of that, whether or not it's "best practice".