I would like to ask for help to improve my skills about test and code quality.
I read a ton of guides and docs and I was not able to find an example of how to do a better code or test in a clean way.
My component has two useRef and it add some listeners to allow the user resize the div element. it works as expected! But I wish to ensure (by tests) that functions onMouseDownRightResize and onMouseMoveRightResize adjust the component using the correct data.
Could someone please show me:
how to test onMouseDownRightResize or onMouseMoveRightResize once the were defined inside the useEffect?
how to test if ref.current is null once he it is inside of the useEffect
Here is my code and a link to a code pen
https://codepen.io/getjv/pen/LYBZPrp
const { useState, useEffect, useRef } = React;
const App = () => {
const ref = useRef(null);
const refRight = useRef(null);
useEffect(() => {
const resizeableEle = ref.current;
if (!resizeableEle) {
return;
}
const styles = window.getComputedStyle(ref.current);
let width = parseInt(styles.width, 10);
let x = 0;
const onMouseMoveRightResize = (event) => {
const dx = event.clientX - x;
x = event.clientX;
width = width + dx;
resizeableEle.style.width = `${width}px`;
};
const onMouseUpRightResize = (event) => {
document.removeEventListener("mousemove", onMouseMoveRightResize);
};
const onMouseDownRightResize = (event) => {
x = event.clientX;
resizeableEle.style.left = styles.left;
resizeableEle.style.right = "";
document.addEventListener("mousemove", onMouseMoveRightResize);
document.addEventListener("mouseup", onMouseUpRightResize);
};
const resizerRight = refRight.current;
if (!resizerRight) {
return;
}
resizerRight.addEventListener("mousedown", onMouseDownRightResize);
return () => {
resizerRight.removeEventListener(
"mousedown",
onMouseDownRightResize
);
};
}, []);
return (
<div className="App">
<div ref={ref} className="flex w-40 border border-red-500 m-5">
<div className="w-full">move the green -> </div>
<div
ref={refRight}
className="bg-green-500 w-2 cursor-col-resize"
></div>
</div>
</div>
);
};
ReactDOM.render(<App />, document.getElementById("app"));
Here I have a simple timer application in React. Do I need to always call cancelAnimationFrame before calling next requestAnimationFrame in animate method?
I read from somewhere that if I call multiple requestAnimationFrame within single callback, then cancelAnimationFrame is required. But in my example, I am calling single requestAnimationFrame in a single callback.
I got even confused when one said no need while another one said need in this article: https://medium.com/#moonformeli/hi-caprice-liu-8803cd542aaa
function App() {
const [timer, setTimer] = React.useState(0);
const [isActive, setIsActive] = React.useState(false);
const [isPaused, setIsPaused] = React.useState(false);
const increment = React.useRef(null);
const start = React.useRef(null);
const handleStart = () => {
setIsActive(true);
setIsPaused(true);
setTimer(timer);
start.current = Date.now() - timer;
increment.current = requestAnimationFrame(animate);
};
const animate = () => {
setTimer(Date.now() - start.current);
cancelAnimationFrame(increment.current);
increment.current = requestAnimationFrame(animate);
};
const handlePause = () => {
cancelAnimationFrame(increment.current);
start.current = 0;
setIsPaused(false);
};
const handleResume = () => {
setIsPaused(true);
start.current = Date.now() - timer;
increment.current = requestAnimationFrame(animate);
};
const handleReset = () => {
cancelAnimationFrame(increment.current);
setIsActive(false);
setIsPaused(false);
setTimer(0);
start.current = 0;
};
return (
<div className="app">
<div className="stopwatch-card">
<p>{timer}</p>
<div className="buttons">
{!isActive && !isPaused ? (
<button onClick={handleStart}>Start</button>
) : isPaused ? (
<button onClick={handlePause}>Pause</button>
) : (
<button onClick={handleResume}>Resume</button>
)}
<button onClick={handleReset} disabled={!isActive}>
Reset
</button>
</div>
</div>
</div>
);
};
ReactDOM.render(<App/>, document.getElementById('root'));
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/17.0.1/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/17.0.1/umd/react-dom.production.min.js"></script>
<div id="root"></div>
No you don't need to cancel the raf in the recursive function, since a raf is just like a setTimeout, but it executes the function in perfect sync with the screen refresh rate, so it executes only once:
const animate = ()=>{
setTimer(Date.now()-start.current)
increment.current = requestAnimationFrame(animate)
}
I have a carousel of slides in my react.js project without using any libraries. When I use an odd amount of images everything works. But when I use even amount, although currentIndex is changing properly only odd images are displayed like 1,3,5 in this example with six images. Can anyone spot what is wrong with my code so it would work with ane amount of images not only with odd ones? Thanks very much
import React from 'react';
import Slide from './Slide';
import img1 from "../assets/img1.jpg";
import img2 from "../assets/img2.jpg";
import img3 from "../assets/img3.jpg";
import img4 from "../assets/img4.jpg";
import img5 from "../assets/img5.jpg";
import img6 from "../assets/img6.jpg";
class Test extends React.Component {
state = {
currentIndex: 0,
images: [img1, img2, img3, img4, img5, img6]
}
prevSlide = () => {
const lastIndex = this.state.images.length - 1;
const resetIndex = this.state.currentIndex === 0;
const index = resetIndex ? lastIndex : this.state.currentIndex - 1;
this.setState({
currentIndex: index
});
};
nextSlide = () => {
const lastIndex = this.state.images.length - 1;
const resetIndex = this.state.currentIndex === lastIndex;
const index = resetIndex ? 0 : this.state.currentIndex + 1;
this.setState({
currentIndex: index
});
};
render() {
const index = this.state.currentIndex;
let newImagesArray = this.state.images.slice(index, index + 6);
if (newImagesArray.length < 6) {
newImagesArray = newImagesArray.concat(
this.state.images.slice(0, 6 - newImagesArray.length)
);
}
return (
<div className="paint__container">
{newImagesArray.map((image, i) =>
this.state.currentIndex === i ? (
<Slide key={i} url={image} alt="" />
) : null
)}
<div className="left__arrow" onClick={this.prevSlide}></div>
<div className="right__arrow" onClick={this.nextSlide}></div>
</div>
);
}
}
export default Test;
okay, thank you for providing the full code, looking at the component on github
we can find
you have nextSlide defined twice, where the second I guess will overwrite the first declaration
while you have the currentIndex in state why you are searching for the target slide in your render function? you don't have to do this my friend, while currentIndex correctly calculate the index then you just render the slide at that index, that's why we are using react after all
render() {
const index = this.state.currentIndex;
const images = this.state.images;
return (
<div className="paint__container">
<Slide url={images[index]} alt="" />
<div className="left__arrow" onClick={this.prevSlide}></div>
<div className="right__arrow" onClick={this.nextSlide}></div>
</div>
);
}
Im trying to build an audio progess bar with react hooks. I was following a tutorial with react class based components but got a little lost with refs.
How can I give my useRef variables an initial value of the div ref when the page loads?
As soon as I start playing then the I get an error saying cant read offsetwidth of null. Obviously timeline ref is null as it doesnt have an initial value. How can I connect it to the div with id of timeline in the useEffect hook?
const AudioPlayer = () => {
const url = "audio file";
const [audio] = useState(new Audio(url));
const [duration, setDuration] = useState(0);
const [currentTime, setCurrentTime] = useState(0)
let timelineRef = useRef()
let handleRef = useRef()
useEffect(() => {
audio.addEventListener('timeupdate', e => {
setDuration(e.target.duration);
setCurrentTime(e.target.currentTime)
let ratio = audio.currentTime / audio.duration;
let position = timelineRef.offsetWidth * ratio;
positionHandle(position);
})
}, [audio, setCurrentTime, setDuration]);
const mouseMove = (e) => {
positionHandle(e.pageX);
audio.currentTime = (e.pageX / timelineRef.offsetWidth) * audio.duration;
};
const mouseDown = (e) => {
window.addEventListener('mousemove', mouseMove);
window.addEventListener('mouseup', mouseUp);
};
const mouseUp = (e) => {
window.removeEventListener('mousemove', mouseMove);
window.removeEventListener('mouseup', mouseUp);
};
const positionHandle = (position) => {
let timelineWidth = timelineRef.offsetWidth - handleRef.offsetWidth;
let handleLeft = position - timelineRef.offsetLeft;
if (handleLeft >= 0 && handleLeft <= timelineWidth) {
handleRef.style.marginLeft = handleLeft + "px";
}
if (handleLeft < 0) {
handleRef.style.marginLeft = "0px";
}
if (handleLeft > timelineWidth) {
handleRef.style.marginLeft = timelineWidth + "px";
}
};
return (
<div>
<div id="timeline" ref={(timeline) => { timelineRef = timeline }}>
<div id="handle" onMouseDown={mouseDown} ref={(handle) => { handleRef = handle }} />
</div>
</div>
)
}
The useRef() hook returns a reference to an object, with the current property. The current property is the actual value useRef points to.
To use the reference, just set it on the element:
<div id="timeline" ref={timelineRef}>
<div id="handle" onMouseDown={mouseDown} ref={handleRef} />
And then to use it, you need to refer to the current property:
let position = current.timelineRef.offsetWidth * ratio;
And positionHandle - you shouldn't actually set styles on elements in React in this way. Use the setState() hook, and set the style using JSX.
const positionHandle = (position) => {
let timelineWidth = timelineRef.current.offsetWidth - handleRef.current.offsetWidth;
let handleLeft = position - timelineRef.current.offsetLeft;
if (handleLeft >= 0 && handleLeft <= timelineWidth) {
handleRef.current.style.marginLeft = handleLeft + "px";
}
if (handleLeft < 0) {
handleRef.current.style.marginLeft = "0px";
}
if (handleLeft > timelineWidth) {
handleRef.current.style.marginLeft = timelineWidth + "px";
}
};
In addition, the ref can be also used for other values, such as the new Audio(url), and be extracted from the current property:
const { current: audio } = useRef(new Audio(url));
I will attempt to keep this brief, but I am not 100% sure of the correct method of achieving what I am aiming for. I have been thrown in the deep end with React with not much training, so I have most likely been going about most of this component incorrectly, a point in the right direction will definitely help, I don't really expect for someone to completely redo my component for me as it's quite long.
I have a navigation bar SubNav, that finds the currently active item based upon the url/path, this will then move an underline element that inherits the width of the active element. To do this, I find the position of the active item and position accordingly. The same goes for when a user hovers over another navigation item, or when the window resizes it adjusts the position accordingly.
I also have it when at lower resolutions, when the nav gets cut off to have arrows appear to scroll left/right on the navigation to view all navigation items.
Also, if on a lower resolution and the currently active navigation item is off screen, the navigation will scroll to that item and then position the underline correctly.
This, currently works as I have it in my component, this issue is, I don't believe I have done this correctly, I am using a lodash function delay to delay at certain points (I guess to get the correct position of certain navigation items, as it isn't correct at the time of the functions call), which I feel is not the way to go. This is all based on how fast the page loads etc and will not be the same for each user.
_.delay(
() => {
setSizes(getSizes()),
updateRightArrow(findItemInView(elsRef.length - 1)),
updateLeftArrow(findItemInView(0));
},
400,
setArrowStyle(styling)
);
Without using the delay, the values coming back from my state are incorrect as they haven't been set yet.
My question is, how do I go about this correctly? I know my code below is a bit of a read but I have provided a CODESANBOX to play about with.
I have 3 main functions, that all sort of rely on one another:
getPostion()
This function finds the active navigation item, checks if it's within the viewport, if it is not, then it changes the left position of the navigation so it's the leftmost navigation item on the screen, and via setSizes(getSizes()) moves the underline directly underneath.
getSizes()
This is called as an argument within setSizes to update the sizes state, which returns the left and right boundaries of all navigation items
getUnderlineStyle()
This is called as an argument within setUnderLineStyle within the getSizes() function to update the position of the underline object in relation to the position of active navigation item grabbed from the sizes state, but I have to pass the sizesObj as an argument in setSizes as the state has not been set. I think this is where my confusion began, I think I was under the impression, that when I set the state, I could then access it. So, I started using delay to combat.
Below is my whole Component, but can be seen working in CODESANBOX
import React, { useEffect, useState, useRef } from "react";
import _ from "lodash";
import { Link, Route } from "react-router-dom";
import "../../scss/partials/_subnav.scss";
const SubNav = props => {
const subNavLinks = [
{
section: "Link One",
path: "link1"
},
{
section: "Link Two",
path: "link2"
},
{
section: "Link Three",
path: "link3"
},
{
section: "Link Four",
path: "link4"
},
{
section: "Link Five",
path: "link5"
},
{
section: "Link Six",
path: "link6"
},
{
section: "Link Seven",
path: "link7"
},
{
section: "Link Eight",
path: "link8"
}
];
const currentPath =
props.location.pathname === "/"
? "link1"
: props.location.pathname.replace(/\//g, "");
const [useArrows, setUseArrows] = useState(false);
const [rightArrow, updateRightArrow] = useState(false);
const [leftArrow, updateLeftArrow] = useState(false);
const [sizes, setSizes] = useState({});
const [underLineStyle, setUnderLineStyle] = useState({});
const [arrowStyle, setArrowStyle] = useState({});
const [activePath, setActivePath] = useState(currentPath);
const subNavRef = useRef("");
const subNavListRef = useRef("");
const arrowRightRef = useRef("");
const arrowLeftRef = useRef("");
let elsRef = Array.from({ length: subNavLinks.length }, () => useRef(null));
useEffect(
() => {
const reposition = getPosition();
subNavArrows(window.innerWidth);
if (!reposition) {
setSizes(getSizes());
}
window.addEventListener(
"resize",
_.debounce(() => subNavArrows(window.innerWidth))
);
window.addEventListener("resize", () => setSizes(getSizes()));
},
[props]
);
const getPosition = () => {
const activeItem = findActiveItem();
const itemHidden = findItemInView(activeItem);
if (itemHidden) {
const activeItemBounds = elsRef[
activeItem
].current.getBoundingClientRect();
const currentPos = subNavListRef.current.getBoundingClientRect().left;
const arrowWidth =
arrowLeftRef.current !== "" && arrowLeftRef.current !== null
? arrowLeftRef.current.getBoundingClientRect().width
: arrowRightRef.current !== "" && arrowRightRef.current !== null
? arrowRightRef.current.getBoundingClientRect().width
: 30;
const activeItemPos =
activeItemBounds.left * -1 + arrowWidth + currentPos;
const styling = {
left: `${activeItemPos}px`
};
_.delay(
() => {
setSizes(getSizes()),
updateRightArrow(findItemInView(elsRef.length - 1)),
updateLeftArrow(findItemInView(0));
},
400,
setArrowStyle(styling)
);
return true;
}
return false;
};
const findActiveItem = () => {
let activeItem;
subNavLinks.map((i, index) => {
const pathname = i.path;
if (pathname === currentPath) {
activeItem = index;
return true;
}
return false;
});
return activeItem;
};
const getSizes = () => {
const rootBounds = subNavRef.current.getBoundingClientRect();
const sizesObj = {};
Object.keys(elsRef).forEach(key => {
const item = subNavLinks[key].path;
const el = elsRef[key];
const bounds = el.current.getBoundingClientRect();
const left = bounds.left - rootBounds.left;
const right = rootBounds.right - bounds.right;
sizesObj[item] = { left, right };
});
setUnderLineStyle(getUnderlineStyle(sizesObj));
return sizesObj;
};
const getUnderlineStyle = (sizesObj, active) => {
sizesObj = sizesObj.length === 0 ? sizes : sizesObj;
active = active ? active : currentPath;
if (active == null || Object.keys(sizesObj).length === 0) {
return { left: "0", right: "100%" };
}
const size = sizesObj[active];
const styling = {
left: `${size.left}px`,
right: `${size.right}px`,
transition: `left 300ms, right 300ms`
};
return styling;
};
const subNavArrows = windowWidth => {
let totalSize = sizeOfList();
_.delay(
() => {
updateRightArrow(findItemInView(elsRef.length - 1)),
updateLeftArrow(findItemInView(0));
},
300,
setUseArrows(totalSize > windowWidth)
);
};
const sizeOfList = () => {
let totalSize = 0;
Object.keys(elsRef).forEach(key => {
const el = elsRef[key];
const bounds = el.current.getBoundingClientRect();
const width = bounds.width;
totalSize = totalSize + width;
});
return totalSize;
};
const onHover = active => {
setUnderLineStyle(getUnderlineStyle(sizes, active));
setActivePath(active);
};
const onHoverEnd = () => {
setUnderLineStyle(getUnderlineStyle(sizes, currentPath));
setActivePath(currentPath);
};
const scrollRight = () => {
const currentPos = subNavListRef.current.getBoundingClientRect().left;
const arrowWidth = arrowRightRef.current.getBoundingClientRect().width;
const subNavOffsetWidth = subNavRef.current.clientWidth;
let nextElPos;
for (let i = 0; i < elsRef.length; i++) {
const bounds = elsRef[i].current.getBoundingClientRect();
if (bounds.right > subNavOffsetWidth) {
nextElPos = bounds.left * -1 + arrowWidth + currentPos;
break;
}
}
const styling = {
left: `${nextElPos}px`
};
_.delay(
() => {
setSizes(getSizes()),
updateRightArrow(findItemInView(elsRef.length - 1)),
updateLeftArrow(findItemInView(0));
},
500,
setArrowStyle(styling)
);
};
const scrollLeft = () => {
const windowWidth = window.innerWidth;
// const lastItemInView = findLastItemInView();
const firstItemInView = findFirstItemInView();
let totalWidth = 0;
const hiddenEls = elsRef
.slice(0)
.reverse()
.filter((el, index) => {
const actualPos = elsRef.length - 1 - index;
if (actualPos >= firstItemInView) return false;
const elWidth = el.current.getBoundingClientRect().width;
const combinedWidth = elWidth + totalWidth;
if (combinedWidth > windowWidth) return false;
totalWidth = combinedWidth;
return true;
});
const targetEl = hiddenEls[hiddenEls.length - 1];
const currentPos = subNavListRef.current.getBoundingClientRect().left;
const arrowWidth = arrowLeftRef.current.getBoundingClientRect().width;
const isFirstEl =
targetEl.current.getBoundingClientRect().left * -1 + currentPos === 0;
const targetElPos = isFirstEl
? targetEl.current.getBoundingClientRect().left * -1 + currentPos
: targetEl.current.getBoundingClientRect().left * -1 +
arrowWidth +
currentPos;
const styling = {
left: `${targetElPos}px`
};
_.delay(
() => {
setSizes(getSizes()),
updateRightArrow(findItemInView(elsRef.length - 1)),
updateLeftArrow(findItemInView(0));
},
500,
setArrowStyle(styling)
);
};
const findItemInView = pos => {
const rect = elsRef[pos].current.getBoundingClientRect();
return !(
rect.top >= 0 &&
rect.left >= 0 &&
rect.bottom <= window.innerHeight &&
rect.right <= window.innerWidth
);
};
const findLastItemInView = () => {
let lastItem;
for (let i = 0; i < elsRef.length; i++) {
const isInView = !findItemInView(i);
if (isInView) {
lastItem = i;
}
}
return lastItem;
};
const findFirstItemInView = () => {
let firstItemInView;
for (let i = 0; i < elsRef.length; i++) {
const isInView = !findItemInView(i);
if (isInView) {
firstItemInView = i;
break;
}
}
return firstItemInView;
};
return (
<div
className={"SubNav" + (useArrows ? " SubNav--scroll" : "")}
ref={subNavRef}
>
<div className="SubNav-content">
<div className="SubNav-menu">
<nav className="SubNav-nav" role="navigation">
<ul ref={subNavListRef} style={arrowStyle}>
{subNavLinks.map((el, i) => (
<Route
key={i}
path="/:section?"
render={() => (
<li
ref={elsRef[i]}
onMouseEnter={() => onHover(el.path)}
onMouseLeave={() => onHoverEnd()}
>
<Link
className={
activePath === el.path
? "SubNav-item SubNav-itemActive"
: "SubNav-item"
}
to={"/" + el.path}
>
{el.section}
</Link>
</li>
)}
/>
))}
</ul>
</nav>
</div>
<div
key={"SubNav-underline"}
className="SubNav-underline"
style={underLineStyle}
/>
</div>
{leftArrow ? (
<div
className="SubNav-arrowLeft"
ref={arrowLeftRef}
onClick={scrollLeft}
/>
) : null}
{rightArrow ? (
<div
className="SubNav-arrowRight"
ref={arrowRightRef}
onClick={scrollRight}
/>
) : null}
</div>
);
};
export default SubNav;
You can make use of useLayoutEffect hook to determine whether the values have been updated and take an action. Since you want to determine whether all the values has been updated, you need to compare old and new values in useEffect. You can refer to the below post to know how to write a usePrevious custom hook
How to compare oldValues and newValues on React Hooks useEffect?
const oldData = usePrevious({ rightArrow, leftArrow, sizes});
useLayoutEffect(() => {
const {rightArrow: oldRightArrow, leftArrow: oldLeftArrow, sizes: oldSizes } = oldData;
if(oldRightArrow !== rightArrow && oldLeftArrow !== leftArrow and oldSizes !== sizes) {
setArrowStyle(styling)
}
}, [rightArrow, leftArrow, sizes])
I think the reason of your delay is necessary here since you calculate based on rectangles of the first and the last element which are affected when you click on button and do animation of scrolling 500ms. So as a result your calculation needs to wait for animation to be done. change the number of animation and delay you will see the relation.
the style I meant.
#include transition(all 500ms ease);
In short, I think what you are using is the right way as long as you have animations related to the calculation.
setState takes an optional second argument which is a callback that executes after the state has been updated and the component has been re-rendered.
Another option is the componentDidUpdate lifecycle method.