Develop Reference

How to calcuclate properties from element sizes in React?

I have a card on my page, which has a title that is the name of a user. The names are sometimes longer than the card, the overflow previously was ellipsis, and a tooltip appeared on hover to show the full name. Now it should be changed in a way, that if it would overflow, then the texts letter-spacing attribute would decrease all the way down to -2, and after that will it start to truly overflow with an ellipsis. How to calculate the values from the available width of the enclosing div? Or how else should it be impemented.
Current state:
For names that can fit with letter-spacing : -2
For long names :
For short names:
Note, container size is the same across all cards!

Let's assume your card component is like this
function Card({ name }) {
return (
<div className="card">
<div className="card__pic"></div>
<h3 className="card__name" ref={nameRef}>
{name}
</h3>
</div>
);
}
All we need is the element containing the name i.e "card__name".
Access the 'name' element.
To access this name element, we have to use useRef hook. Here's how you would use it.
function Card({ name }) {
const nameRef = useRef(null);
useEffect(() => {
// nameRef.current is accessible here
}, []);
return (
<div className="card">
<div className="card__pic"></div>
<h3 className="card__name" ref={nameRef}>
{name}
</h3>
</div>
);
}
We have to pass ref={refVariable} to the element we'd like to access.
The refVariable will be initialized with the element node after mount i.e we can use it inside the useEffect hook.
Determine if the name is overflowing.
Now since we have the element, we can use it to check if the text inside is overflowing. I've created a function isTextOverflowingCard to which we pass the reference to the element we get after mount. It will return true if it text is overflowing else false.
function isTextOverflowingCard(textElement) {
if (textElement.scrollWidth > textElement.clientWidth) {
return true;
}
return false;
}
Now inside Card we can use this function and based on its return value, add a class conditionally which will have the tight letter-spacing value.
function Card({ name }) {
const nameRef = useRef(null);
const [textOverflow, setTextOverflow] = useState(false);
useEffect(() => {
// nameRef.current is accessible here
setTextOverflow(isTextOverflowingCard(nameRef.current));
}, []);
return (
<div className="card">
<div className="card__pic"></div>
<h3 className={`card__name ${textOverflow ? 'card__name--tight-kerning' : ''}`} ref={nameRef}>
{name}
</h3>
</div>
);
}
In CSS,
.card__name--tight-kerning {
letter-spacing: -2px;
}
You can change useEffect to useLayoutEffect, which is better suited for such dom related calculations and applying to ui.
References:
Detect if text has overflown
useEffect vs useLayoutEffect
https://reactjs.org/docs/hooks-reference.html#useref

How can I add styling to an element in React?

In normal JavaScript you can grab an element by its id and add a style to it.
For example:
var element = document.getElementById("myElement");
element.style.backgroundColor = "#f5f5f5";
My question is how you can do this in react. Is it even possible to add this style?
In react im using onChange in a function outside the render(). I looked at the React DOM for styling and tried but since styling is in different function it will tell me how the variable is undefined.
this is my code:
ChangeImage() {
var imgStyles = {
backgroundColor: '#000',
padding: 5,
}
}
render() {
return (
<div className="class">
<div className="img-surround">
<img
src={this.state.file}
id="img"
style={imgStyles}/>
</div>
Everything is working except styles and I even tried putting in different functions

If you want to render the element with the style you can return the element like this in a react functional component:
return <div style={{backgroundColor: "#f5f5f5"}}></div>
If you want the element to only have that style in a certain condition you can use the useState hook in a react functional component:
const [myState, setMyState] = useState(false);
return <div style={myState && {backgroundColor: "f5f5f5"}}></div>
And you should change myState's value using setMyState however you like. For example:
const [myState, setMyState] = useState(false);
return <div onClick={() => myState ? setMyState(true) : setMyState(false)} style={myState && {backgroundColor: "f5f5f5"}}></div>
In this example whenever you click on the div the style is added or removed by case

React add html attribute to external component

I am using a component that I cannot change directly, but I would like to extend.
import { Button } from '#external-library'
// Currently how the button component is being used
<Button click={() => doSomething()} />
// I would like to add a tabIndex to the button
<Button click={() => doSomething()} tabIndex={0} />
I cannot add an attribute because the component is not expecting a tabIndex. I cannot directly modify the Button component.
How can I extend the <Button /> component so I can add attributes like tabIndex, etc?
I was hoping something like the following would work:
export default class ExtendedButton extends Button { }
// except I'm dealing with functional components

You can't edit custom component implementation without changing its internals.
// You can't add tabIndex to internal button without changing its implementation
const Button = () => <button>Click</button>;
In such cases, you implement a wrapper with desired props:
const Component = () => {
return (
<div tabIndex={0}>
<Button />
</div>
);
};
If the component forwarding ref (also depends to which element it forwarded in the implementation), you can use its attributes:
// Assumption that Button component forwards ref
const Button = React.forwardRef((props,ref) => <button ref={ref}>Click</button>);
<Button ref={myRef}/>
// Usage
myRef.current.tabIndex = 0;

You can access the inner DOM button element using React refs(read here)
most likely the external-lib you use provide a ref prop for the Button component which you use to pass your own create ref
const buttonRef = useRef(null);
<Button ref={buttonRef}/>
Then you can use buttonRef.current to add tabIndex when your data is ready to be populated in like
useEffect( () => {
if(buttonRef && buttonRef.current){
buttonRef.current.tabIndex = 2;
}
}, [props.someProperty] );

How to access the DOM element of the child component in Preact with hooks?

I am using Preact with hooks. I have following button component:
export function Button(props) {
return (
<button class={props.class}>{props.children}</button>
);
}
I have another parent component where I need to access actual DOM element button for animation purpose.
export function Parent(props) {
const buttonElm = useRef(null);
useEffect(() => {
console.log(buttonElm.current);
// Animate button using popmotion or similar
});
return (
<div>
<Button ref={buttonElm}>Click me to animate</Button>
</div>
);
}
However, there is a problem. The buttonElm.current points to JSX object i.e. Button but not the DOM element button. I need buttonElm to point to actual DOM element. How do I do that?
Should I go ahead and use buttonElm.current.base property? But that does not feel idiomatic with hooks.
Also, I have two questions.
How does ref behave when I am setting it on a Preact component that returns multiple elements using <Fragment />.
Second, is accessing the children's DOM element for animation purpose acceptable/correct practice in Preact/React? (I can wrap my component in another wrapper div but that causes more animation headaches than solving the problem)

You need to pass ref as props to your child component. By doing this buttonElm will point to actual Button DOM element.
export function Button(props) {
return (
<button class={props.class} ref={props.buttonElm}>{props.children}</button>
);
}
export function Parent(props) {
const buttonElm = useRef(null);
useEffect(() => {
console.log(buttonElm.current);
// Animate button using popmotion or similar
});
return (
<div>
<Button buttonElm={buttonElm}>Click me to animate</Button>
</div>
);
}

react-dnd DragSource that has child DragSource

I have a tree structure with a root "Tree" component that has a list of root "TreeNodes", then TreeNodes can have an arbitrary number of children.
So inside of the TreeNode render method I have
childrenHTML = this.state.children.map((child) => {
return (<TreeNode nodeClick ={this.props.nodeClick} parentNode={this}
key={child.childId} node={child} level={this.state.level+1} />);
});
and
const { isDragging, connectDragSource, connectDragPreview} = this.props;
Then the final return for the render method looks like
return connectDragSource(
<div>
<div style={nodeStyle}>
{connectDragPreview(
<div className = {"nodeContainer" + ' ' + this.state.nodeHover} onMouseLeave={this.nodeUnHover} onMouseOver={this.nodeHover} onClick={()=>this.props.nodeClick(this)}>
<img alt = {this.state.titleIcon} className = "titleIcon" src = {Connections.getImageURLByName(this.state.titleIcon)} />
<p className="nodeLabel"> {this.state.nodeName}</p>
{nodeLabelsHTML}
<DescriptiveIcons descriptiveIcons={this.state.icons} />
</div>
)}
</div>
{childrenHTML}
</div>
);
I am exporting:
export default DragSource(DragTypes.STRUCTURE, treeNodeSource, collect)(TreeNode);
Then in the parent Tree file I am exporting
export default DragDropContext(HTML5Backend)(Tree)
and rendering the rootnodes like
rootNodesHTML = rootNodes.map((node) => {
return <TreeNode nodeClick={this.props.nodeClick} key={node.childId} node={node} level={0}/>
});
...
return (
<div className="treeContainer">
<div className="wrapContainer">
{rootNodesHTML}
</div>
</div>
);
This works great but only for the rootnodes, when I try to render the children (the childrenHTML variable is only populated after the parent is clicked on) I get the following error:TypeError: connectDragPreview is not a function
Leading me to believe that those react-dnd props that come from the "collect" function is not being passed to the rootnodes but not the children. It seems like it should to me because the same code should be executed for the parents as for the children as its the same class... really stuck here.
I am relatively new to react, and new to ideas like HOCs so all tips or suggestions are appreciated. Thank you!

I was able to get this working. Check out the example posted at the end of the thread in
https://github.com/react-dnd/react-dnd/issues/332.
Ultimately the solution was to wrap the TreeNode in a "DragContainer" with a very simple render method
render(){
const {...props} = this.props;
return <TreeNode {...props}/>
}
Then in the TreeNode render method, when rendering the child nodes render a DragContainer instead, passing in all the usual props.
childrenHTML = this.state.children.map((child) => {
return <DragNodeContainer modalFunctions = {this.props.modalFunctions} nodeClick ={this.props.nodeClick} parentNode={this} key={child.childId} node={child} level={this.state.level+1} />;
});
I am still unsure as to the technical reason for this, however, the fix seems to work for other people and it works for me!