Develop Reference

Javascript splice array method is not working as expected

,
I was working out with splice methods of js , but as it may seem it was not working exactly as it should remove any element from an array .
Currently its only deleting the last element from array even after providing the index value for it to delete from the array. in console.log i get the perfect output after deleting anything , but in UI part it does not update as it should , its only removing the last element from array even if i click on delete other item . How can i resolve this ?
Here's what i've tried so far :
const add_actions_options = [
{value : "Postback" , label:intl.formatMessage({ id: 'POSTBACK' })},
{value : "Uri" , label:intl.formatMessage({ id: 'URI' })}
]
const [ actions , setActions ] = useState<any | undefined>([{type : add_actions_options[0].value , label : "" , data : ""}])
const [selectOptions, setSelectOptions] = useState<any>(add_actions_options);
function addAction(){
if(actions.length < 4 ){
setSelectOptions([...add_actions_options])
setActions([...actions , {type : selectOptions[0].value , label : "" , data : ""}])
} else {
toast(intl.formatMessage({ id: 'MAX.ALLOWED.4' }), { type: "error" })
}
}
function deleteAction(index){
if(actions.length === 1 ){
toast(intl.formatMessage({ id: 'MIN.ALLOWED.1' }), { type: "error" })
} else {
const updatedFields = [...actions];
updatedFields.splice(index, 1);
console.log('index : ' , index)
console.log('updatedFields : ' , updatedFields)
setActions(updatedFields);
}
}
<div className='row my-6'>
<div className='col-lg-3 py-2'>
<h4><label className="form-label">{intl.formatMessage({ id: 'ACTIONS' })}*</label></h4>
<button className='btn btn-primary btn-sm btn-block' onClick={() => addAction()}>
<KTSVG path='/media/icons/duotune/arrows/arr075.svg' className='svg-icon-2' />
{intl.formatMessage({id: 'ADD.ACTION'})}
</button>
</div>
</div>
<div className='row my-6 '>
{ actions.map((item , index) => {
return(
<div key={index} className='row my-6'>
<div className='col-lg-4 py-2'>
<h4><label className="form-label">{intl.formatMessage({ id: 'TEMPLATE.TYPE' })}*</label></h4>
<Select
onChange={(value) => handleTypeChange(index, value)}
options={selectOptions}
/>
</div>
<div className='col-lg-3 py-2'>
<h4><label className="form-label">{intl.formatMessage({ id: 'TEMPLATE.LABEL' })}*</label></h4>
<input
{...formik_buttons_type.getFieldProps('action.label')}
className="form-control form-control-lg form-control-solid"
name='action.label'
id='action_label'
type="text"
maxLength={30}
onChange={(event) => handleLabelChange(index, event.target.value)}
value={actions.label}
required
onInvalid={(e) => checkLabelValidation(e)}
onInput={(e) => checkLabelValidation(e)}
/>
</div>
<div className='col-lg-3 py-2'>
<h4><label className="form-label">{intl.formatMessage({ id: 'TEMPLATE.DATA' })}*</label></h4>
<input
{...formik_buttons_type.getFieldProps('action.data')}
className="form-control form-control-lg form-control-solid"
name='action.data'
id='action_data'
type="text"
maxLength={100}
onChange={(event) => { handleDataChange(index, event.target.value); }}
value={actions.data}
required
onInvalid={(e) => checkDataValidation(e)}
onInput={(e) => checkDataValidation(e)}
/>
</div>
<div className='col-lg-2 py-2 mt-10'>
<OverlayTrigger
delay={{ hide: 50, show: 50 }}
overlay={(props) => (
<Tooltip {...props}>
{intl.formatMessage({ id: 'DEL.ACTION' })}
</Tooltip>
)}
placement="top">
<button
type='button'
style={{display: index === 0 ? 'none': 'inline-block'}}
className='btn btn-icon btn-md btn-bg-light btn-color-danger me-1'
onClick={() => deleteAction(index)}
>
<i className='fa fa-trash'></i>
</button>
</OverlayTrigger>
</div>
</div>
)
})}
</div>
I am able to receive exact index number perfect output from the logs below in deleteAction fields , but the view in browser deletes the last column(index) from the array of actions. :
console.log('index : ' , index)
console.log('updatedFields : ' , updatedFields)
can anyone help me with this ?
code sand box : https://codesandbox.io/s/vibrant-christian-bktnot
Thanks and Regards !

Whenever using the index as a key for an element. We have to ensure we are not modifying the state array to avoid bugs. If you are modifying as #Dave suggested use unique keys.
The problem here is using the index as key, When we remove an element from an array react compares the previous keys [0,1,2,3] with new keys [0,1,2].
If you notice closely, Even if we remove index (1) using splice(1,1) method. The elements which are rendered again have starting index of 0.
React compares keys previous keys [0,1,2,3] with new keys [0,1,2] and finds out that index 3 is removed hence it every time removes the 3rd element in the above example (or the last index) from DOM. However, your state is reflecting the correct array element.
To avoid this use a unique key.
Codesandbox for a working example.
If you are not having keys in objects, To generate unique keys we can use one of the following as per your use case:
crypto.randomUUID();
Date.now().toString(36) + Math.random().toString(36).substr(2)

https://reactjs.org/docs/lists-and-keys.html
We don’t recommend using indexes for keys if the order of items may change. This can negatively impact performance and may cause issues with component state.
When you do
{ actions.map((item , index) => {
return(
<div key={index}
you are pretty much asking for issues with component state. When react is trying to determine which element in the UI to update, and it sees "the array with a length of 6 now has a length of 5, which element do I need to remove", it will find the one with a key that no longer exists, in this case the one at the end since you used index as key, and will remove it.
I would probably do
function randomId(){
const uint32 = window.crypto.getRandomValues(new Uint32Array(1))[0];
return uint32.toString(16);
}
const [ actions , setActions ] = useState<any | undefined>([{id: randomId(), type : add_actions_options[0].value , label : "" , data : ""}])
function addAction(){
if(actions.length < 4 ){
setSelectOptions([...add_actions_options])
setActions([...actions , {id: randomId(), type : selectOptions[0].value , label : "" , data : ""}])
} else {
toast(intl.formatMessage({ id: 'MAX.ALLOWED.4' }), { type: "error" })
}
}
{ actions.map((item) => {
return(
<div key={item.id}
where randomId can be anything that gives you a unique ID, or (even better) if there is an existing property on the actual data that uniquely identifies it, you could use that.

React native conditional rendering an array with 2 conditions

I have an array with several objects. Inside each object i have a field called type that can be either a or b. I am trying to conditional render a specific view for type a and a specific view for type b.
Here is my array:
DATA=[
{id:1, type:'a'},{id:2,type:'b'}
]
return(
{DATA.type === 'a' ?
<Text>I am type A</Text>
:
<Text>I am Type B </Text>
}
)
When i do that nothing appears on the screen.
UPDATE
DATA=[
{id:1, type:'a',locked:true},
{id:2,type:'b',locked:false}
]
const[isLocked,setIsLocked]=useState(false)
return(
{isLocked && DATA.map((item) => item.type === 'a')) ?
<Text>I am type A</Text>
:
null}
)
it is still not working. I am type A still appears on all pages of my carousel.

You need to map your array to accomplish it. Otherwise, you can't get the correct key.
DATA = [
{ id:1, type:a },
{ id:2, type:b },
]
return(
DATA.map((item) => item.type === 'a'
? <Text>I am type A</Text>
: <Text>I am Type B </Text>
))

"react" Each child in a list should have a unique "key" prop

An error seems to occur because the key value is not entered in the map function, but I do not know how to modify the code.
The array is structured like this:
const tabContArr=[
{
tabTitle:(
<span className={activeIndex===0 ? "is-active" : ""} onClick={()=>tabClickHandler(0)}>0</span>
),
},
{
tabTitle:(
<span className={activeIndex===1 ? "is-active" : ""} onClick={()=>tabClickHandler(1)}>1</span>
),
},
{
tabTitle:(
<span className={activeIndex===2 ? "is-active" : ""} onClick={()=>tabClickHandler(2)}>2</span>
),
},
{
tabTitle:(
<span className={activeIndex===3 ? "is-active" : ""} onClick={()=>tabClickHandler(3)}>3</span>
),
}
];
An error occurs in the map function part.
{tabContArr.map((section)=>{
return section.tabTitle
})}

Try with React Fragments with a key attribute as mentioned in React docs
{tabContArr.map((section, index)=>{
return <React.Fragment key={`section-tab-${index}`}>{section.tabTitle}</React.Fragment>
})}

What you have done is not the right way.
If you have data, instead of passing the ReactElement into the array you should pass it into the map function like this:
{tabContArr.map((tab, index)=>{
return <span
className={activeIndex === index ? "is-active" : ""}
onClick={()=>tabClickHandler(index)}
key={`tab-${index}`}>index</span>
})}

Can I change the order of li elements conditionally in React

I have a list with side menu options, some of them are normal categories, some of them are static, here is my code:
//const type = the type is either categories or static
{items.map((item, index) => {
return (
<li>
{type !== 'categories' ? (
<> Static </>
) : (
<> Category </>
)}
</li>
);
})}
So in the items that are of type static I have a variable that comes from the back end which is called display, its value could be either 'top' or 'bottom', what I want to do is, if the type is equal to 'static', to move the order of the li to the value item.display has, for example:
<li>----</li> //type static //item.display: top
<li>++++</li> //type static //item.display: bottom
<li>""""</li> //type categories //item.display doesn't exist here
<li>::::</li> //type categories //item.display doesn't exist here
In the example above the li filled with the symbol '+' has a value of display: bottom,
so it should go to the bottom of the list and the list should now look like that:
<li>----</li> //type static //item.display: top
<li>""""</li> //type categories //item.display doesn't exist here
<li>::::</li> //type categories //item.display doesn't exist here
<li>++++</li> //type static //item.display: bottom
How can I implement that logic, I already tried doing it with inline styles like so:
<li style={{order: item.display === "top" ? items.length.toString() : "1"}}>
I am not even sure if this is a viable HTML, but it didn't work anyway, what are your suggestions for solving this problem?

You can control the order using items.sort() before you map it into virtual dom nodes.
Example:
import React from 'react'
function App() {
let items = [
{ text: '----', type: 'static', display: 'top' },
{ text: '++++', type: 'static', display: 'bottom' },
{ text: '""""', type: 'categories' },
{ text: '::::', type: 'categories' },
]
return (
<ul>
{items
.sort((a, b) =>
a.display === b.display
? 0
: a.display === 'top'
? -1
: a.display === 'bottom'
? 1
: 0,
)
.map(item => (
<li>
{item.type !== 'categories' ? (
<> Static </>
) : (
<> Category </>
)}
</li>
))}
</ul>
)
}
export default App
output:
<ul>
<li>----</li>
<li>""""</li>
<li>::::</li>
<li>++++</li>
</ul>

A possible solution would be that you have a mapping from string to number and a little helper function
const displayMap = {
top: 0,
default: 1,
bottom: 2
};
const compareDisplay(a,b){
let disp1 = a.display ?? 'default';
let disp2 = b.display ?? 'default';
return displayMap[disp1] > displayMap[disp2] ? 1 : -1;
}
in case if display is not defined, it will take default, which is mapped to the middle value
In case display also contains other values than top or bottom, you need to add a bit of logic to the helper function
you can use this mapping, to sort your objects before mapping
{
items.sort((a,b) => compareDisplay(a,b)).map((item, index) => {
return (
<li>
{
type !== 'categories' ?
(<> Static </>) :
(<> Category </>)
}
</li>
);
})}

Using onClick to call the same function works for one thing and not another?

I'm creating an application where a user can search for a device with a search bar, or look through a nested menu. When the user finds the device they want, they click on the green plus to add it to their "bag". For some reason the addDevice function I've written only works for the search function, and not when it's called in the menu. It seems to partially work, but not correctly. Does anyone know what in my code could be causing this? Please see the images below for more details.
I'm also making two different API calls, one for the search bar (called in its own function) and one for the menu (called in componentDidMount). Could this possibly be what's causing the error?
I won't include every line of code because it's a lot, but please let me know if you'd like to see anything else.
class App extends React.Component {
state = {
devices: [],
bag: [],
objectKeys: null,
tempKeys: []
};
this is the function that gets called by the onClick's
addDevice = (e, deviceTitle) => {
const array = Array.from(this.state.bag || []);
if (array.indexOf(deviceTitle) === -1) {
array.push(deviceTitle);
} else {
return;
}
localStorage.setItem("list", JSON.stringify(array));
this.setState({
bag: array
});
};
This is the function that doesn't seem to work when addDevice is called
makeMenuLayer = layer => {
const { objectKeys } = this.state;
if (layer == null) {
return null;
}
const layerKeys = Object.entries(layer).map(([key, value]) => {
{/*If value has children, display an arrow, if not, do nothing*/}
var arrow = Object.keys(value).length ? (
<i
className="fas fa-angle-right"
style={{ cursor: "pointer", color: "gray" }}
/>
) : (
""
);
{/*If value has no children, display an plus sign, if not, do nothing*/}
var plus =
Object.keys(value).length === 0 ? (
<i
className="fas fa-plus"
style={{ cursor: "pointer", color: "green" }}
onClick={e => this.addDevice(e, this.value)}
/>
) : (
""
);
return (
<ul key={key}>
<div onClick={() => this.handleShowMore(key)}>
{key} {arrow} {plus}
</div>
{objectKeys[key] && this.makeMenuLayer(value)}
</ul>
);
});
return <div>{layerKeys}</div>;
};
this is where the addDevice that does work gets called
render () {
return(
<div className="search-results">
{(this.state.devices || []).map(device => (
<a key={device.title}>
<li>
{device.title}{" "}
<i
className="fas fa-plus plus input"
style={{ cursor: "pointer", color: "green" }}
onClick={e => this.addDevice(e, device.title)}
/>
</li>
</a>
))}
</div>
)}
This is what it looks like when devices are added from the search (works fine)
This is what happens when I try to add "Necktie" from the menu. It doesn't let me add anything else after that

In this line onClick={e => this.addDevice(e, this.value)}
The value of this points to the class itself. Thus, this.value is undefined, It's not not allowing you to add anything more because undefined is already in the array and undefined === undefined is actually true.
To fix this, you need to pass the correct value of the device title.