Using React JSX, I have an array levels which can contain arrays of one or more of the levels with a name, for example: one, two and three. In my render function I can call {renderLevels} which renders all levels separated by a comma.
This works:
const renderLevels = levels.map((item, index) => {
return (
<Fragment key={index}>
{(index ? ' & ' : '')} {item.name}
</Fragment>
)
}
);
In case all levels are present I want to render 'all levels', instead of the comma separated list. In all other cases I want the list. So I change my code.
This does not work:
const renderLevels = () => {
if (levels.length === 3) {
return (
'all levels'
)
}
levels.map((item, index) => {
return (
<Fragment key={index}>
{(index ? ' & ' : '')} {item.name}
</Fragment>
)
}
)
};
My const is now a function I then call with {renderLevels()}. The problem: the list of item names is no longer returned when there are fewer than 3 levels. My if-statement works and console.log(item.name) inside .map does show me the results in case there are fewer than 3 levels. Getting the return values however does not. What am I doing wrong?
You are missing return for the levels.map(). Currently, you are just returning for the function, inside the if block but you have not returned anything when that if is not executed.
const renderLevels = () => {
if (levels.length === 3) {
return (
'all levels'
)
}
return levels.map((item, index) => {
return (
<Fragment key={index}>
{(index ? ' & ' : '')} {item.name}
</Fragment>
)
}
)
};
Related
I am trying to refactor my code and in doing so, I am extracting a single item and putting it into its own component. This MemberItem component has multiple functions state that influence its rendering, however, when I start passing props, the component breaks. I am passing all of the functions, properties and state the the child component needs, but I am still unable to get it to render properly.
// Members.js (Parent Component)
export const Members = () => {
// BELOW ARE THE FUNCTIONS AND STATE THAT INFLUENCE THE CHILD COMPONENT
const [memberName, setMemberName] = useState('')
const [editingMemberName, setEditingMemberName] = useState(
members.map(() => false)
)
// Update member name
const editMemberName = async (_, index) => {
let new_editing_members_state = members.map(() => false)
new_editing_members_state[index] = true
setEditingMemberName(new_editing_members_state)
}
// Cancel editing mode
const cancelEditMemberName = async (_, index) => {
let new_editing_members_state = members.map(() => false)
new_editing_members_state[index] = false
setEditingMemberName(new_editing_members_state)
}
// UPDATE name in database
const updateMemberName = async (index, id) => {
let new_editing_members_state = members.map(() => false)
new_editing_members_state[index] = false
setEditingMemberName(new_editing_members_state)
}
// BELOW, LOOPS OVER EACH ITEM
const memberItems = members.map((member, index) => {
return (
<MemberItem
member={member}
index={index}
editingMemberName={editingMemberName[index]}
editMemberName={editMemberName}
handleChangeName={handleChangeName}
updateMemberName={updateMemberName}
cancelEditMemberName={cancelEditMemberName}
destroyMember={destroyMember}
/>
)
})
return (
// RENDER THE LIST OF ITEMS
{memberItems}
)
}
// Member.js (Child Component)
export const MemberItem = (
member,
index,
editingMemberName,
editMemberName,
handleChangeName,
updateMemberName,
cancelEditMemberName,
destroyMember
) => {
return (
<div
key={member.id}
>
<div>
{editingMemberName[index] ? (
<input
type="text"
placeholder="Johnny Appleseed"
onChange={handleChangeName}
/>
) : (
<>
<div>
{member.name.substring(0, 1).toUpperCase()}
</div>
<h3>{member.name}</h3>
</>
)}
</div>
<div>
{editingMemberName[index] ? (
<button
onClick={() => updateMemberName(index, member.id)}
>
<CgCheckO size=".75em" />
</button>
) : (
<button
onClick={() => editMemberName(member.id, index)}
>
<FiTool size=".75em" />
</button>
)}
<button>
{editingMemberName[index] ? (
<GiCancel
onClick={() => cancelEditMemberName(member.id, index)}
size=".75em"
/>
) : (
<RiDeleteBinLine
onClick={() => destroyMember(member.id)}
size=".75em"
/>
)}
</button>
</div>
</div>
)
}
Currently, I am getting an error of TypeError: editingMemberName is undefined and a warning of Each child in a list should have a unique "key" prop, but if you see, I do pass in an id into the key property.
In React, props are passed down to function components as a single object.
Your component function assumes props are passed down as separate arguments and not in a single object.
Fixed component definition (note the brackets around the argument list):
MemberItem = ({
member,
index,
editingMemberName,
editMemberName,
handleChangeName,
updateMemberName,
cancelEditMemberName,
destroyMember
}) => { ... }
This method of unpacking properties is called object destructuring.
I have this response object from an api, and I want to loop it and render it as if it was a normal array, how can I render tshirt, jeans and furniture? I will not like to render the value of sneakers, Any suggestion?
const items = {
tshirt: "Model TS",
jeans: "ModelXW",
sneakers: "indcdsc54",
furniture: "Table31S"
};
{Object.keys(items).map=>{i =>
<Card>
{items[key]}
</Card>
}
}
Try this one implementation line:
{Object.entries(items).filter(v => v[0] !== 'sneakers').map((v, idx) => <Card key={idx}>v[1]</Card>)}
You can read properties of an object using dynamic key: objectName[keyName]:
{
Object.keys(items).map(key => <Card key={key}>{items[key]}</Card>)
}
and to filter out sneakers:
{Object.keys(items).filter(key => key !== 'sneakers').map((key) => (
<Card key={key}>{items[key]}</Card>
))}
Instead of multiple loops, add an if condition to your code:
Object.keys(items).map(key => {
if (key != 'sneakers') {
return(<Card>{items[key]}</Card>);
}
});
We can use destructuring and it is definitely more readable.
const { sneakers, ...rest } = items;
Object.keys(rest).map((item, id) => {
<Card key={id}>
{item}
</Card>
}
);
I trying to generate a big form based on what I get from the server.
sometimes I generate 32 elements sometimes 57 or 4 I don't know.
I try to create a component for each type of element like select, text, number, textarea and so on.
each component passes the value to the parent component and setState the value to the parent.
imagine I have 20 inputs and custom select-option elements.
when I type something in one of the inputs characters show up after 2seconeds and there is a huge lag in my component.
I know because of the setState method my hole component (I mean my parent component or my single source of truth) re-renders and causes the problem.
in fact, I don't know other ways.
I try to use a "this.VARIABLE" and instead of setState, I update the "this.VARIABLE" and problem solved. but I need my state.
any help or solution?
my code (parent Component, source of truth ):
// ---> find my component based on the type that I get from server
findComponent ( item , index) {
if ( item.type === 'text' || item.type === 'number') {
return (<Text data={item} getUpdated={this.fetchingComponentData} />);
} else if ( item.type === 'longtext') {
return (<Textarea data={item} getUpdated={this.fetchingComponentData} />);
} else if ( item.type === 'select' ) {
return (<SelectOption data={item} getUpdated={this.fetchingComponentData} />);
} else if ( item.type === 'autocomplete') {
return (<AutoTag data={item} url={URL1} getUpdated={this.fetchingComponentData} />);
} else if ( item.type === 'checkbox_comment' ) {
return (<CheckboxComment data={item} getUpdated={this.fetchingComponentData} />);
} else if ( item.type === 'multiselect' ) {
return (<Multiselect data={item} getUpdated={this.fetchingComponentData} />);
} else {
return (<p>THERE IS NO TYPE OF => {item.type}</p>);
}
}
// ----> if i setState here ==> big lag
fetchingComponentData(OBJ) {
let index = null;
// let Answer = [...this.state.Answer];
index = Helper.find_item(this.Answer , OBJ , 'unique_key');
if ( index === -1 ) {
this.Answer.push(OBJ);
} else {
this.Answer[index].value = OBJ.value;
}
}
// ----> in my render method
render () {
return (
<React.Fragment>
<div className="row Technical section" data-info="Technical">
<div className="col-6">
{data.map( (item,index) => {
return (
<React.Fragment key={index}>
<div className="rowi">
{item.attributes.map( (item, index)=> {
return <React.Fragment key={index}>{this.findComponent(item, index)}</React.Fragment>;
})}
</div>
</React.Fragment>
)
})}
</div>
<div className="col-6"></div>
</div>
</React.Fragment>
);
}
Have you tried to make an object out of your components and pass it to setState at once?
const nextState = componentList.map(component => {
return {[component]: value};
});
this.setState({...nextState});
Edit: Okay i got another part you could do better.
You should build an array with you components in componentWillMount function instead of fetching all the data inside the render. Like you said, it's updating everytime any state changes, and all the components are also updating with the parent.
This is to be made in addition with what I suggested before, but it is of far more importance because of the impact on the ressource.
I have a product component that renders n number of sections. The code in the product component:
let sections = this.state.product.sections.map((section, idx) => {
return (
<Section sectionType={section.id} section={section} />
)
})
return (
<div>
{this.state.product.name}
{sections}
</div>
)
The code in the section component:
renderSection() {
switch (this.props.sectionType) {
case 'heroImage':
return (
<img src={image.url} />
)
case 'doublePane':
this.props.section.items.map((item, idx) => {
console.log(item.id);
if (1 === 1) {
return (
<div>hi</div>
)
}
})
default:
return (
<div>hey there</div>
)
}
}
render() {
return (
<div>
{this.renderSection()}
</div>
)
}
I added the 1===1 line just to make sure it would execute, but the output of my code is still
the heroImage case properly executes
the console log of item.id happens (so we definitely enter the doublePane block), but the code inside of the 1===1 block does not execute.
Any idea what's happening here to not allow me to run the code inside of the 1===1? Thanks in advance!
You need to return the result of the mapping function, in addition to returning within the mapping function:
renderSection() {
switch (this.props.sectionType) {
case 'heroImage':
return (
<img src={image.url} />
);
case 'setOfTwo':
return (
<div>
{this.props.section.items.map((item, idx) => {
console.log(item.id);
return (
<div>hi</div>
);
})}
</div>
);
default:
return (
<div>hey there</div>
)
}
}
Wrapping the return value in a div isn't necessarily required, but I prefer to return a consistent item (in this case a single JSX element) from functions.
I am trying to render an objects key and value, however it just doesn't seem to work.
I have managed to display it in the console, but not the actual dom.
I am iterating through the object which has multiple entries.
What do I need to do to actually print out the values?
{attributes.map(items => {
{Object.keys(items).map((key) => {
console.log(key, items[key]);
})}
})}
Like this:
{attributes.map((items, index) => {
return (
<ul key={index}>
{Object.keys(items).map((key) => {
return (
<li key={key + index}>{key}:{items[key]}</li>
)
})}
</ul>
)
})}