I'm curioused about the work of this code.
It's a simple code, I intended to raise counter for 1 and print on console.
but when I click the button the counter increases, also printing from 0 ~ to all the number that I increased.
run screenshot
Could you explain why this happens?
import { useState } from "react";
function App() {
const [counter, setCounter] = useState(0);
const onClick = () => {
window.addEventListener("click", () => {
console.log(counter);
});
setCounter((counter) => counter + 1);
};
return (
<div className="App">
<button onClick={() => onClick()}>Add & Print!</button>
<div>{counter}</div>
</div>
);
}
export default App;
You added onClick event to button tag and when the function is executed, onClick event to window is added. So whenever clicking button tag, addEventListener that order to add shows console.log is made. On the code, showing console.log doesn't need addEventListener because button tag already has onClick event.
In <button onClick={() => onClick()}>Add & Print!</button> tag, onClick event is executed whenever the tag is clicked,
Below,
window.addEventListener("click", () => {
console.log(counter);
});
addEventListener adds event.
So whenever clicking button tag, addEventListener is executed(that adds events).
import { useState } from "react";
function App() {
const [counter, setCounter] = useState(0);
const onClick = () => {
// doesn't need window.addEventListener
// window.addEventListener("click", () => {
console.log(counter);
// });
setCounter((counter) => counter + 1);
};
return (
<div className="App">
<button onClick={() => onClick()}>Add & Print!</button>
<div>{counter}</div>
</div>
);
}
export default App;
On every click you are adding an event listener. So on first click there is one event listener, on second 2, on third three and so on. (on nth click, n event listeners are there on window object).
There is also the situation of the event listener using stale state. The window event listener has closed over(closures) the old value of state and is logging it. So the first event listener is always using count = 0. The third event listener is using count = 2. So, on.
Related
I have search about this problem.
It must be pass function reference.
document.addEventListener("click", () => {}, false)
But what I do is still fire immediately.
Do I make some wrong?
Test code is below
export default function App() {
const start = () => {
console.log("start");
};
const click1 = () => {
document.addEventListener("click", start);
};
const click2 = () => {
const element = document.getElementById("p");
element.addEventListener("click", start);
};
return (
<div className="App">
<h1>Hello CodeSandbox</h1>
<button onClick={click1}>Click1</button>
<hr />
<p id="p">123</p>
<button onClick={click2}>Click2</button>
</div>
);
}
// Click1 - immediately, problem here
// Click2 - no immediately
https://codesandbox.io/s/reverent-grass-5fok7b?file=/src/App.js
What I expect
click first, add click event, no anything is log.
click second, log 'start'
actually output
click first, add click event, log start.
You're handling a SyntheticEvent with your onClick handler and adding a native event listener at the document level. Adding the listener will complete before the event bubbles up to the top therefore you also see it execute for the original event.
If you don't want that to happen, stop the event from bubbling
const click1 = (e) => {
e.stopPropagation();
document.addEventListener("click", start);
};
FYI, you should also remove the DOM listener when your component unmounts
useEffect(() => () => document.removeEventListener("click", start), []);
Another option you might consider, keeping in mind the React paradigm to only attach listeners using React when possible, would be to attach the click handler to your App, rather than to the document with .addEventListener. (Best to only use addEventListener when there's no alternative with React handlers.)
function App() {
const [started, setStarted] = React.useState(false);
const tryLog = () => {
if (started) {
log();
}
};
const log = () => console.log("event");
return (
<div className="App" onClick={tryLog}>
<h1>Hello CodeSandbox</h1>
<button onClick={() => setStarted(true)}>Click1</button>
<hr />
<p id="p">123</p>
<button onClick={log}>Click2</button>
</div>
);
}
ReactDOM.createRoot(document.querySelector('.react')).render(<App />);
<script crossorigin src="https://unpkg.com/react#18/umd/react.development.js"></script>
<script crossorigin src="https://unpkg.com/react-dom#18/umd/react-dom.development.js"></script>
<div class='react'></div>
TL/DR: My simple toggle function fires twice when button is clicked.
I'm using useEffect in a React (w/ Next.js) component so that I can target the :root <html> tag for which I need the class to be toggled. The code is the following:
useEffect(() => {
const toggleMode = () => {
const root = document.documentElement;
root.classList.toggle("dark");
console.log("click");
};
const toggleBtn = document.querySelector("#toggle-btn");
toggleBtn.addEventListener("click", toggleMode);
I have the necessary imports, the code is placed inside the main component function before the return, and there's no errors in the console at all.
The only issue is that the function is fired twice every time the button is clicked and I cannot find any reason why or solutions online.
Would really appreciate your help and please let me know if I'm missing any information.
Cheers!
Your problem is coming from registering the event listener in a non-react way.
By registering the listener via
const toggleBtn = document.querySelector("#toggle-btn");
toggleBtn.addEventListener("click", toggleMode);
you are setting up a new listener each time the function is run, even if the DOM is not updated. This could result in multiple listeners being registered and firing simultaneously.
You need to add your listener the react way.
function Component ( props ){
const [ isFirst, setIsFirst ] = useState( true );
const [ toggle, setToggle ] = useState( false );
useEffect(() => {
if( isFirst ) {
setIsFirst( false );
return;
}
document.documentElement.classList.toggle("dark");
}, [ toggle ] );
return <div>
<button id="toggle-btn" onClick = { e => setToggle( !toggle ) } />
</div>
}
I resolved a similar problem in this post: Why does my NextJS Code run multiple times, and how can this be avoided?
Your code should only run once if you disable react strict mode.
Code Sandbox here
Hi, I want to create a container so that if you click the button inside of the container, a box appears. I have added an event listener so that if you mouse out of the container, the box will no longer show. Of course, I need to also add an event listener to the button inside of the container so that hovering over the button won't hide the box if you have the box already visible.
However, I am having difficulty with this and am seeing some side effects. For example, if you as click the button to show the box, and then click it again to hide the box, then hovering over the button will show the box again, which is not the desired affect.
I believe there is something I am doing wrong using React.useEffect and not tracking state properly, but I am unsure.
When writing a useEffect that manually adds some kind of event listener, 99% of the time you must have it return a cleanup function that will remove said event listener. Otherwise you end up with dangling event listeners that haven't been cleaned up between useEffect calls.
React.useEffect(() => {
const handleButtonMouseOver = (): void => {
if (show) {
setShow(true);
}
};
// const handleMouseOut = (): void => {
// if (show) {
// setShow(false);
// }
// };
// Save reference to this element in the scope of the function
// buttonRef.current may change between triggers
const buttonElement = buttonRef.current;
if (buttonElement) {
buttonElement.addEventListener("mouseover", handleButtonMouseOver);
}
// if (containerRef.current) {
// containerRef.current.addEventListener("mouseout", handleMouseOut);
// }
// Add this
return () => {
buttonElement.removeEventListener("mouseover", handleButtonMouseOver);
};
}, [buttonRef, containerRef, show]);
https://reactjs.org/docs/hooks-effect.html#effects-with-cleanup
I have a modal dialog that I want to close if the user clicks outside of the modal. I have written the following useEffect code but I run into following issue:
The modal dialog contains a number of children (React Nodes) and those children might change (e.g. the user deletes an entry of a list). Those interactions trigger my onClick method but as the clicked list item has been removed from the modal, the modal closes even though the click was within the modal.
I thought adding [ children ] at the second parameter for useEffect would cleanup the old effect event listener quick enough that the method does not run again but this is not the case.
I handled the same issue in a class component with a ignoreNextClick-state but there must be a cleaner solution, right?
useEffect( () => {
const onClick = ( event ) => {
const menu = document.getElementById( 'singleton-modal' );
if ( !menu ) return;
// do not close menu if user clicked inside
const targetInMenu = menu.contains( event.target );
const targetIsMenu = menu === event.target;
if ( targetInMenu || targetIsMenu ) return;
onCloseModal();
};
window.addEventListener( 'click', onClick, false );
return () => window.removeEventListener( 'click', onClick, false );
}, [ children ] );
I found a solution that does not require any sort of storing old props.
The useEffect call looks like this:
useEffect( () => {
const onClickOutside = () => onCloseModal();
window.addEventListener( 'click', onClickOutside, false );
return () => window.removeEventListener( 'click', onClickOutside );
}, [] );
Adding the following click listener to the modal directly will stop the window click-listener from being called if the user clicked inside the modal.
<div
className={`modal ${ classes }`}
onClick={event => event.stopPropagation()}
role="presentation"
>
{children}
</div>`
I also added the role presentation to make the modal more accessible and aria-conform.
You can check parent of modal from the event.target.
If the current target is within the modal then return.
You can use closest to do that.
See the following solution.
...
if (event.target.closest( '.singleton-modal' ) || event.target.classList.contains('singleton-modal')) {
return;
}
...
The bounty expires in 7 days. Answers to this question are eligible for a +50 reputation bounty.
ajaykools wants to reward an existing answer:
Worth bounty, only way simulate clicks on dynamic elements like svg, g, circle, etc which are generated on page load.
I'm trying to simulate a .click() event on a React element but I can't figure out why it is not working (It's not reacting when I'm firing the event).
I would like to post a Facebook comment using only JavaScript but I'm stuck at the first step (do a .click() on div[class="UFIInputContainer"] element).
My code is:
document.querySelector('div[class="UFIInputContainer"]').click();
And here's the URL where I'm trying to do it: https://www.facebook.com/plugins/feedback.php...
P.S. I'm not experienced with React and I don't know really if this is technically possible. It's possible?
EDIT: I'm trying to do this from Chrome DevTools Console.
React tracks the mousedown and mouseup events for detecting mouse clicks, instead of the click event like most everything else. So instead of calling the click method directly or dispatching the click event, you have to dispatch the down and up events. For good measure I'm also sending the click event but I think that's unnecessary for React:
const mouseClickEvents = ['mousedown', 'click', 'mouseup'];
function simulateMouseClick(element){
mouseClickEvents.forEach(mouseEventType =>
element.dispatchEvent(
new MouseEvent(mouseEventType, {
view: window,
bubbles: true,
cancelable: true,
buttons: 1
})
)
);
}
var element = document.querySelector('div[class="UFIInputContainer"]');
simulateMouseClick(element);
This answer was inspired by Selenium Webdriver code.
With react 16.8 I would do it like this :
const Example = () => {
const inputRef = React.useRef(null)
return (
<div ref={inputRef} onClick={()=> console.log('clicked')}>
hello
</div>
)
}
And simply call
inputRef.current.click()
Use refs to get the element in the callback function and trigger a click using click() function.
class Example extends React.Component{
simulateClick(e) {
e.click()
}
render(){
return <div className="UFIInputContainer"
ref={this.simulateClick} onClick={()=> console.log('clicked')}>
hello
</div>
}
}
ReactDOM.render(<Example/>, document.getElementById('app'))
<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="app"></div>
If you don't define a class in your component, and instead you only declare:
function App() { ... }
In this case you only need to set up the useRef hook and use it to point/refer to any html element and then use the reference to trigger regular dom-events.
import React, { useRef } from 'react';
function App() {
const inputNameRef = useRef()
const buttonNameRef = useRef()
function handleKeyDown(event) {
// This function runs when typing within the input text,
// but will advance as desired only when Enter is pressed
if (event.key === 'Enter') {
// Here's exactly how you reference the button and trigger click() event,
// using ref "buttonNameRef", even manipulate innerHTML attribute
// (see the use of "current" property)
buttonNameRef.current.click()
buttonNameRef.current.innerHTML = ">>> I was forced to click!!"
}
}
function handleButtonClick() {
console.log('button click event triggered')
}
return (
<div>
<input ref={inputNameRef} type="text" onKeyDown={handleKeyDown} autoFocus />
<button ref={buttonNameRef} onClick={handleButtonClick}>
Click me</button>
</div>
)
}
export default App;
A slight adjustment to #carlin.scott's great answer which simulates a mousedown, mouseup and click, just as happens during a real mouse click (otherwise React doesn't detect it).
This answer adds a slight pause between the mousedown and mouseup events for extra realism, and puts the events in the correct order (click fires last). The pause makes it asynchronous, which may be undesirable (hence why I didn't just suggest an edit to #carlin.scott's answer).
async function simulateMouseClick(el) {
let opts = {view: window, bubbles: true, cancelable: true, buttons: 1};
el.dispatchEvent(new MouseEvent("mousedown", opts));
await new Promise(r => setTimeout(r, 50));
el.dispatchEvent(new MouseEvent("mouseup", opts));
el.dispatchEvent(new MouseEvent("click", opts));
}
Usage example:
let btn = document.querySelector("div[aria-label=start]");
await simulateMouseClick(btn);
console.log("The button has been clicked.");
Note that it may require page focus to work, so executing in console might not work unless you open the Rendering tab of Chrome DevTools and check the box to "emulate page focus while DevTools is open".
Inspired from previous solution and using some javascript code injection it is also possibile to first inject React into the page, and then to fire a click event on that page elements.
let injc=(src,cbk) => { let script = document.createElement('script');script.src = src;document.getElementsByTagName('head')[0].appendChild(script);script.onload=()=>cbk() }
injc("https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js",() => injc("https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js",() => {
class ReactInjected extends React.Component{
simulateClick(e) {
e.click()
}
render(){
return <div className="UFIInputContainer"
ref={this.simulateClick} onClick={()=> console.log('click injection')}>
hello
</div>
}
}
ReactDOM.render(<ReactInjected/>, document.getElementById('app'))
} ))
<div id="app"></div>
Kind of a dirty hack, but this one works well for me whereas previous suggestions from this post have failed. You'd have to find the element that has the onClick defined on it in the source code (I had to run the website on mobile mode for that). That element would have a __reactEventHandlerXXXXXXX prop allowing you to access the react events.
let elem = document.querySelector('YOUR SELECTOR');
//Grab mouseEvent by firing "click" which wouldn't work, but will give the event
let event;
likeBtn.onclick = e => {
event = Object.assign({}, e);
event.isTrusted = true; //This is key - React will terminate the event if !isTrusted
};
elem.click();
setTimeout(() => {
for (key in elem) {
if (key.startsWith("__reactEventHandlers")) {
elem[key].onClick(event);
}
}
}, 1000);
Using React useRef Hooks you can trigger a click event on any button like this:
export default const () => {
// Defining the ref constant variable
const inputRef = React.useRef(null);
// example use
const keyboardEvent = () => {
inputRef.current.handleClick(); //Trigger click
}
// registering the ref
return (
<div ref={inputRef} onClick={()=> console.log('clicked')}>
hello
</div>
)
}
This answer was inspired by carlin.scott code.
However, it works only with focusin event in my case.
const element = document.querySelector('element')
const events = ['mousedown', 'focusin']
events.forEach(eventType =>
element.dispatchEvent(
new MouseEvent(eventType, { bubbles: true })
)
)