How to fire function when the variables are set in a useEffect? - javascript

i have a function calculateDistance which calculate when the child component is in the center of the parent component. I want to fire the function on the onScroll event. But the variables I need for it a set in a useEffect and cannot use outside that scope. Has anyone an idea how to fix this?
export function Portfolio() {
const portfolioRef = React.useRef(null)
React.useEffect(() => {
portfolioRef.current.scrollTop = 100
}, []
)
return (
<div className={cx(styles.component, styles.scrollWrapper)}>
<div className={styles.topIcon} dangerouslySetInnerHTML={{ __html: arrow }} />
<div ref={portfolioRef} onScroll={calculateDistance} className={styles.scroll}>
<PortfolioItem
{...{ portfolioRef }}
title='Article about Kaliber Academie'
text='I wrote an article about my experience at Kaliber'
link='https://medium.com/kaliberinteractive/hoe-technologie-het-hart-van-een-luie-scholier-veranderde-3cd3795c6e33'
linkTekst='See Article' />
<PortfolioItem
{...{ portfolioRef }}
title='Article about Kaliber Academie'
text='hola'
link='#'
linkTekst='#' />
<PortfolioItem
{...{ portfolioRef }}
title='Article about Kaliber Academie'
text='hola'
link='#'
linkTekst='#' />
<PortfolioItem
{...{ portfolioRef }}
title='Article about Kaliber Academie'
text='hola'
link='#'
linkTekst='#' />
</div>
<div className={styles.bottomIcon} dangerouslySetInnerHTML={{ __html: arrow }} />
</div>
)
}
export function PortfolioItem({ text, title, link, linkTekst, portfolioRef }) {
const portfolioItemRef = React.useRef(null)
React.useEffect(() => {
const element = portfolioItemRef.current
const parent = portfolioRef.current
}, [portfolioRef])
return (
<div ref={portfolioItemRef} className={styles.componentItem}>
<div className={styles.title}>{title}</div>
<div className={styles.content}>
<div className={styles.text}>{text}</div>
<div className={styles.links}>
<a className={styles.linkTekst} href={link}>{linkTekst} </a>
<div className={styles.linkIcon} dangerouslySetInnerHTML={{ __html:arrow }} />
</div>
</div>
</div>
)
}
function calculateDistance(parent, element) {
if (!parent || !element) return 0
const parentRect = parent.getBoundingClientRect()
const parentCenter = (parentRect.top + parentRect.bottom) / 2
const elementRect = element.getBoundingClientRect()
const elementCenter = (elementRect.top + elementRect.bottom) / 2
const distance = Math.abs(parentCenter - elementCenter)
return clamp(distance / (parentRect.height / 2), 0, 1)
}

It doesnt look as if your calculated distance is being stored anywhere. You probably want the calulateDistance function to update a state variable which you refer to in Portfolio's useEffect.
You can create new variables from your component props and use useState(). you can then update them and reference them in your jsx and changing them will trigger your useEffect(), as long as you have it bounded correctly. Using props directly will only trigger your unbounded useEffect on the initial load. Additionally the reference you made 'portfolioItemRef' is only set when rendered and using it as the bound for the useEffect will not update to the calculated distance as is. move the calculated distance function into the portfolio component.
For Example:
const [stateText, setStateText] = useState(text)
useEffect(()=>{console.log('do something')},[stateText]);
here is a helpful explanation: https://medium.com/better-programming/tips-for-using-reacts-useeffect-effectively-dfe6ae951421

Best thing you can do is listen for the scroll event inside the useEffect
remove the onScroll attached to element
....
<div ref={portfolioRef} className={styles.scroll}>
....
inside useEffect
React.useEffect(() => {
const calculateDistance = (parent, element) => {
if (!parent || !element) return 0
const parentRect = parent.getBoundingClientRect()
const parentCenter = (parentRect.top + parentRect.bottom) / 2
const elementRect = element.getBoundingClientRect()
const elementCenter = (elementRect.top + elementRect.bottom) / 2
const distance = Math.abs(parentCenter - elementCenter)
return clamp(distance / (parentRect.height / 2), 0, 1)
}
//attach event listener
portfolioRef.current.addEventListener("scroll", calculateDistance);
return () => {
// remove the event listener when component unmounts
portfolioRef.current.removeEventListener("scroll", calculateDistance);
}
}, [])
Demo
you have to decide how to get the parent and element inside the calculateDistance

Related

Can you set Mouse hover to identify different elements in React?

I wanted to adapt this code show that, for example if you hovered over a specific , then the relating would also show. useState seems to be the only way to make this work in React as I tried a different example with eventlistner which crashed the page.
const Showstuff = () => {
const [isHovering, setIsHovering] = useState(false);
const handleMouseOver = () => {
setIsHovering(true);
};
const handleMouseOut = () => {
setIsHovering(false);
};
return(
<div>
<div onMouseOver={handleMouseOver} onMouseOut={handleMouseOut}>
Hover over div #1 here
</div><br /><br />
<div>
Hover over div #2 here
</div>
{isHovering && (
<div>
<h2>Text here visible when hovering div 1</h2>
</div>
)}
</div>
)
};
export default Showstuff;
I made multiple useStates for each items as a work around, but this means there's 3x const lines for each item I want to add, and I have 6 elements to hover. Can this be combined into a shorter code? I also tried:
const el = document.getElementById('container');
const hiddenDiv = document.getElementById('hidden-div');
el.addEventListener('mouseover', function handleMouseOver() {
hiddenDiv.style.visibility = 'visible';
});
el.addEventListener('mouseout', function handleMouseOut() {
hiddenDiv.style.visibility = 'hidden';
});
from a guide on bobbyhadz website but this would require the same idea of making multiple lines of the same code with different names. This works immediately after saving the page in vscode but then shortly afterwards crashes the page, and does not work - I assume it is not React compatible.
I would do something like this :
function App() {
const [isHovered, setIsHovered] = useState(null)
const handleMouseOver = (e) => {
switch (e.target.id) {
case "1":
setIsHovered(1)
break
case "2":
setIsHovered(2)
break
}
}
return (
<div className="App">
<div id="1" onMouseOver={handleMouseOver} onMouseOut={() => setIsHovered(null)}>
DIV 1
</div>
<div id="2" onMouseOver={handleMouseOver} onMouseOut={() => setIsHovered(null)}>
DIV 2
</div>
{isHovered && <h2>{isHovered === 1 ? "Div 1 is hovered" : "Div 2 is hovered"}</h2>}
</div>
)
}
That way you only use one useState hook and set the value of isHovered depending on the targetted div's id.
Instead of having isHovering be a boolean, make it something else. If your design means you can only hover one thing at a time, the simplest solution is to make isHovering just hold some ID. But if you have overlapping elements where it's possible to hover multiple at once, you can use an array of IDs, or an object where each key is an ID and each value is a boolean.
You need to modify your onMouseOver (and, possibly, onMouseOut) function(s) to pass an ID as an argument.
Here is a simple example:
const Showstuff = () => {
const [isHovering, setIsHovering] = useState();
const handleMouseOver = (id) => setIsHovering(id);
const handleMouseOut = () => setIsHovering();
return (
<div>
{[1, 2, 3, 4, 5, 6].map((n) => (
<>
<div
onMouseOver={() => handleMouseOver(n)}
onMouseOut={handleMouseOut}
>
{`Hover over div #${n} here`}
</div>
</>
))}
{isHovering && (
<div>
<h2>{`Text here visible when hovering div ${isHovering}`}</h2>
</div>
)}
</div>
);
};
You don't have to use a map function if that won't work for you. That's just what I'm doing in this example. Just make sure your IDs are unique.
If you need to be able to hover multiple items at once, you'll have to modify the handleMouseOver and handleMouseOut functions. For example, if you wanted to store the values in an array, you can do something like this:
const handleMouseOver = (id) =>
setIsHovering((oldIsHovering) => [...oldIsHovering, id]);
const handleMouseOut = (id) =>
setIsHovering((oldIsHovering) => oldIsHovering.filter((n) => n !== id));
You can use an array as a state variable and map over it:
export default function App() {
const [isHovering, setIsHovering] = useState(new Array(4).fill(false));
function handleMouseEnter(i) {
setIsHovering((prev) => {
const next = [...prev];
next[i] = true;
return next;
});
}
function handleMouseLeave(i) {
setIsHovering((prev) => {
const next = [...prev];
next[i] = false;
return next;
});
}
return (
<>
{isHovering.map((_, i) => (
<span
onMouseEnter={() => handleMouseEnter(i)}
onMouseLeave={() => handleMouseLeave(i)}
></span>
))}
{isHovering.map((v, i) => (
<p>
Hovering on {i}: {v.toString()}
</p>
))}
</>
);
}
https://stackblitz.com/edit/react-ts-owprrr?file=App.tsx
This is good if the HTML elements are the same. If all your elements are unique, you are better off using multiple states and naming them uniquely. You'll just end up making the design more confusing by trying to save a few lines of code.

React tab-like system using CSS classes

I have 5 div's and 5 buttons. On each button clicked one div become visible. the other four gets hidden. I just want to ask is there any other better way to do it. Give suggestion as much as possible. Thank you!
let id1 = React.createRef()
let id2 = React.createRef()
let id3 = React.createRef()
let id4 = React.createRef()
let id5 = React.createRef()
function iid1() {
id1.current.classList.remove('hidden')
id1.current.classList.add('contents')
id2.current.classList.add('hidden')
id3.current.classList.add('hidden')
id4.current.classList.add('hidden')
id5.current.classList.add('hidden')
}
function iid2() {
id1.current.classList.add('hidden')
id2.current.classList.remove('hidden')
id2.current.classList.add('contents')
id3.current.classList.add('hidden')
id4.current.classList.add('hidden')
id5.current.classList.add('hidden')
}
function iid3() {
id1.current.classList.add('hidden')
id2.current.classList.add('hidden')
id3.current.classList.remove('hidden')
id3.current.classList.add('contents')
id4.current.classList.add('hidden')
id5.current.classList.add('hidden')
}
function iid4() {
id1.current.classList.add('hidden')
id2.current.classList.add('hidden')
id3.current.classList.add('hidden')
id4.current.classList.remove('hidden')
id4.current.classList.add('contents')
id5.current.classList.add('hidden')
}
function iid5() {
id1.current.classList.add('hidden')
id2.current.classList.add('hidden')
id3.current.classList.add('hidden')
id4.current.classList.add('hidden')
id5.current.classList.remove('hidden')
id5.current.classList.add('contents')
}
I just want the above code to be more efficient & readable. I'm looking for best practices for javascript. You can also tell me you would you solve this problem. I'm not looking for answer's. I'm here to seek best practices,
Thank you.
Use state to identify which div is the selected one. Buttons will change the state and your app will re-render adjusting the classNames for the divs.
const App = () => {
const [selected,setSelected] = React.useState(0);
const DIV_IDS = [0,1,2,3,4,5];
const selectItems = DIV_IDS.map((item) => {
return(
<button onClick={() => setSelected(item)}>{item}</button>
);
});
const divItems = DIV_IDS.map((item) => {
return (
<div key={item} className={selected === item ? 'visible' : 'hidden'}>
I am div {item}
</div>
);
});
return(
<div>
<div>{selectItems}</div>
<div>{divItems}</div>
</div>
);
};
ReactDOM.render(<App/>, document.getElementById('root'));
.hidden {
visibility: hidden;
}
.visible {
visibility: visible;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.8.3/umd/react-dom.production.min.js"></script>
<div id="root"></div>
May be best to just have the class in your JSX element classes. Something like:
<element className={(condition_for_shown) ? 'contents' : 'hidden'}>
...
</element>
and then for each button would be:
<button type="button" onClick={() => setStateConditonToSomething}>
...
</button>
Note that you'll need to store the condition in react state with useState or however you wanna store it.
The way i'd do it is -
const DivHidingComponent = ({ elementCount = 5 }) => { // element count defaults to 5
const [visibilityIndex, setVisibilityIndex] = useState(0);
const onClickCallback = useCallback((index) => () => {
setVisibilityIndex(index);
})
const buttonGroup = useMemo(() => {
const buttonGroup = [];
for (let i = 0; i < elementCount; i++) {
buttonGroup.push(
<button key={`${i}-button`} onClick={onClickCallback(i)} />
)
}
return buttonGroup;
}, [elementCount])
// only re-runs on a button click
const divGroup = useMemo(() => {
const divGroup = [];
for (let i = 0; i < elementCount; i++) {
divGroup.push(
<div key={`${i}-div`} style={{ visibility: visibilityIndex === i ? 'visible' : 'hidden' }} />
);
}
return divGroup;
}, [visibilityIndex]);
return (
<div>
<div>
{buttonGroup}
</div>
<div>
{divGroup}
</div>
</div>
);
}
I set the style directly in the div group loop, but you could assign a class name or go about setting the style however you want.
Div's visibility is set by the visibility index that is driven by the buttons being clicked on.
I passed the elementCount variable in the props so you could scale this to however many elements you want. 5 or a 1000. I assigned elementCount a value of 5 that will act as a default for when no value is passed when the component is initialized.
Also, you could drop the useMemo and useCallback hooks and it would still execute fine. But it would help improve performance if you say, set the element count to 10,000. With those hooks in place it'd only re-build the div group on re-render. That'd be the difference between running the loops 20k times (10k for buttons, 10k for divs).
I added the last paragraph incase you were not aware of React Hooks!
I hope this helps!

React .scrollLeft cannot be reading null value

I am trying to access the horizontal scroll bar with buttons in react but turns out it is not working because of error that cannot read the null values of .scrollLeft.
<>
<div className="containerOuterSider">
<FaAngleLeft className= "FaAngleLeft" onClick={slide('left')}/>
<div id="container3" className="container3">
{products &&
products
.map((product) => (
<AAsOfLowNav key={product._id} product={product} />
))
.reverse()}
</div>
<FaAngleRight className="FaAngleRight" onClick={slide('right')}/>
</div>
</>
and the main function is
function slide(direction) {
var container = document.getElementById('container3');
let scrollCompleted = 0;
var slideVar = setInterval(function() {
if (direction === 'left') {
container.scrollLeft -= 10;
} else {
container.scrollLeft += 10;
}
scrollCompleted += 10;
if (scrollCompleted >= 100) {
window.clearInterval(slideVar);
}
}, 50);
}
The error I am facing is:
Uncaught TypeError: Cannot read properties of null (reading
'scrollLeft')
at LowerCatNav.js:31:1 Uncaught TypeError: Cannot read properties of null (reading 'scrollLeft')
at LowerCatNav.js:33:1
How can I make it right? Should I use the hooks or anything else?
Issue
You are immediately invoking the slide function while rendering:
<FaAngleLeft
className="FaAngleLeft"
onClick={slide('left')} // <-- immediately invoked when rendered
/>
...
<FaAngleRight
className="FaAngleRight"
onClick={slide('right')} // <-- immediately invoked when rendered
/>
The React component hasn't been fully rendered and pushed to the DOM, so queries to the DOM, i.e. document.getElementById('container3'), return null.
Solution
Fix the click handler so slide is not being immediately invoked.
<FaAngleLeft
className="FaAngleLeft"
onClick={() => slide('left')} // <-- asynchronously invoked when clicked
/>
...
<FaAngleRight
className="FaAngleRight"
onClick={() => slide('right')} // <-- asynchronously invoked when clicked
/>
It is considered a React anti-pattern to directly query the DOM for DOMNodes, use a React ref for this.
Example:
...
const containerRef = React.useRef(); // <-- (1) create Ref
const sliderTimerRef = React.useRef();
useEffect(() => {
return () => {
// clear any running intervals on component unmount
clearInterval(sliderTimerRef.current);
};
}, []);
...
function slide(direction) {
// clear any previously set intervals and reset scrollCompleted
clearInterval(sliderTimerRef.current);
let scrollCompleted = 0;
sliderTimerRef.current = setInterval(function() {
const container = containerRef.current; // <-- (3) access current ref value
if (direction === 'left') {
container?.scrollLeft -= 10; // <-- (4) Optional Chaining null check
} else {
container?.scrollLeft += 10; // <-- (4) Optional Chaining null check
}
scrollCompleted += 10;
if (scrollCompleted >= 100) {
clearInterval(sliderTimerRef.current);
}
}, 50);
}
...
return (
<>
<div className="containerOuterSider">
<FaAngleLeft className="FaAngleLeft" onClick={() => slide('left')}/>
<div
ref={containerRef} // <-- (2) attach ref to element
id="container3"
className="container3"
>
{products
.map((product) => (
<AAsOfLowNav key={product._id} product={product} />
))
.reverse()
}
</div>
<FaAngleRight className="FaAngleRight" onClick={() => slide('right')}/>
</div>
</>
);
slide is called when #container3 is not yet created.
Change onClick={slide(...)} to onClick={() => slide(...)}
Access to global elements (e.g. by id) should be avoided.
Prefer ref/createRef/useRef to access elements belonging to your component.

How to get element properties in reactjs

I'm trying to get the height of the parent container element, to use as a height of an SVG background element.
Is there a way to get and pass this property?
I keep getting "TypeError: Cannot read property 'refs' of undefined"
const Services = ({ classes }) => {
return (
<div className={classes.Container} ref="container">//Element I want the height of
<div className={classes.BGContainer}>
<BGSVG width={'210'} height={this.refs.container.height} color={'blue'} />//Where I want to pass height to
</div>
<div className={classes.Services}>
{services.map((e, i) => (
<ServiceItem
title={e.title}
icon={e.icon}
info={e.info}
inverted={i % 2 === 1 ? true : false}
/>
))}
</div>
</div>
);
In a functional component, you need to use the React Hook called useRef like this:
const TextInputWithFocusButton = (props) => {
const inputEl = useRef(null);
const onButtonClick = () => {
// `current` points to the mounted text input element
inputEl.current.focus();
};
return (
<>
<input ref={inputEl} type="text" />
<button onClick={onButtonClick}>Focus the input</button>
</>
);
}
you will see if you log out inputEl that a reference to the input element is logged. DOM element references allow you to access most properties of the particular DOM element referenced.
You haven't bound "this". Try height={() => this.refs.container.height}
If your Services component is inside lets say ServicesWrapper Component, what you should do is put on it
`servicesWrapperContainerRef = React.createRef()`;
Then, on JSX of wrapper component place
`ref={this.servicesWrapperContainerRef}`
and then, pass that as a prop to the Services component like this
const Services = ({ classes, servicesWrapperContainerRef }) and then you can use it to find out the parents height
`height={this.props.servicesWrapperContainerRef.current.clientHeight}`

Is there a way to set the initial height of an element in Reactjs?

I have a react component that allows for a resizable text area based on the text inside.
return (<div className={`resizable-textbox ${className}`}>
<textarea
value={value}
onChange={onChangeMade}
onBlur={onBlur}
readOnly={readOnly} />
</div>);
The onChangeMade method looks like this:
const onChangeMade = (e) => {
const scrollHeightPadded = e.target.scrollHeight;
if ((scrollHeightPadded + "px") !== e.target.style.height) {
e.target.style.height = 0;
const height = Math.max(scrollHeightPadded, 31) + 3;
e.target.style.height = `${height}px`;
}
}
This is a slightly ugly method I know, needs cleaning up. However I want to call this method once on the first load of the component but e is an event triggered by the textarea tag.
Is there a way to hook into this or directly into the component with the method? (I am using React Hooks and stateless components).
Thanks.
You can use createRef to create a ref and give it to the ref prop of your textarea and use that instead of the event.
Example
class MyComponent extends React.Component {
ref = React.createRef();
componentDidMount() {
this.onChangeMade();
}
onChangeMade = () => {
const { current } = this.ref;
const scrollHeightPadded = current.scrollHeight;
if (scrollHeightPadded + "px" !== current.style.height) {
current.style.height = 0;
const height = Math.max(scrollHeightPadded, 31) + 3;
current.style.height = `${height}px`;
}
};
render() {
return (
<div className={`resizable-textbox ${className}`}>
<textarea
ref={this.ref}
value={value}
onChange={onChangeMade}
onBlur={onBlur}
readOnly={readOnly}
/>
</div>
);
}
}

Categories

Resources