I am making a React app that allows you to make a list and save it, but React has been giving me a warning that my elements don't have a unique key prop (elements List/ListForm). How should I create a unique key prop for user created elements? Below is my React code
var TitleForm = React.createClass({
handleSubmit: function(e) {
e.preventDefault();
var listName = {'name':this.refs.listName.value};
this.props.handleCreate(listName);
this.refs.listName.value = "";
},
render: function() {
return (
<div>
<form onSubmit={this.handleSubmit}>
<input className='form-control list-input' type='text' ref='listName' placeholder="List Name"/>
<br/>
<button className="btn btn-primary" type="submit">Create</button>
</form>
</div>
);
}
});
var ListForm = React.createClass({
getInitialState: function() {
return {items:[{'name':'item1'}],itemCount:1};
},
handleSubmit: function(e) {
e.preventDefault();
var list = {'name': this.props.name, 'data':[]};
var items = this.state.items;
for (var i = 1; i < items.length; i++) {
list.data.push(this.refs[items[i].name]);
}
this.props.update(list);
$('#'+this.props.name).remove();
},
handleClick: function() {
this.setState({
items: this.state.items.concat({'name':'item'+this.state.itemCount+1}),
itemCount: this.state.itemCount+1
});
},
handleDelete: function() {
this.setState({
itemCount: this.state.itemCount-1
});
},
render: function() {
var listItems = this.state.items.map(function(item) {
return (
<div>
<input type="text" className="list-form" placeholder="List Item" ref={item.name}/>
<br/>
</div>
);
});
return (
<div>
<form onSubmit={this.handleSubmit} className="well list-form-container">
{listItems}
<br/>
<div onClick={this.handleClick} className="btn btn-primary list-button">Add</div>
<div onClick={this.handleDelete} className="btn btn-primary list-button">Delete</div>
<button type="submit" className="btn btn-primary list-button">Save</button>
</form>
</div>
)
}
});
var List = React.createClass({
getInitialState: function() {
return {lists:[], savedLists: []};
},
handleCreate: function(listName) {
this.setState({
lists: this.state.lists.concat(listName)
});
},
updateSaved: function(list) {
this.setState({
savedLists: this.state.savedLists.concat(list)
});
},
render: function() {
var lst = this;
var lists = this.state.lists.map(function(list) {
return(
<div>
<div key={list.name} id={list.name}>
<h2 key={"header"+list.name}>{list.name}</h2>
<ListForm update={lst.updateSaved} name={list.name}/>
</div>
</div>
)
});
var savedLists = this.state.savedLists.map(function(list) {
var list_data = list.data;
list_data.map(function(data) {
return (
<li>{data}</li>
)
});
return(
<div>
<h2>{list.name}</h2>
<ul>
{list_data}
</ul>
</div>
)
});
var save_msg;
if(savedLists.length == 0){
save_msg = 'No Saved Lists';
}else{
save_msg = 'Saved Lists';
}
return (
<div>
<TitleForm handleCreate={this.handleCreate} />
{lists}
<h2>{save_msg}</h2>
{savedLists}
</div>
)
}
});
ReactDOM.render(<List/>,document.getElementById('app'));
My HTML:
<div class="container">
<h1>Title</h1>
<div id="app" class="center"></div>
</div>
There are many ways in which you can create unique keys, the simplest method is to use the index when iterating arrays.
Example
var lists = this.state.lists.map(function(list, index) {
return(
<div key={index}>
<div key={list.name} id={list.name}>
<h2 key={"header"+list.name}>{list.name}</h2>
<ListForm update={lst.updateSaved} name={list.name}/>
</div>
</div>
)
});
Wherever you're lopping over data, here this.state.lists.map, you can pass second parameter function(list, index) to the callback as well and that will be its index value and it will be unique for all the items in the array.
And then you can use it like
<div key={index}>
You can do the same here as well
var savedLists = this.state.savedLists.map(function(list, index) {
var list_data = list.data;
list_data.map(function(data, index) {
return (
<li key={index}>{data}</li>
)
});
return(
<div key={index}>
<h2>{list.name}</h2>
<ul>
{list_data}
</ul>
</div>
)
});
Edit
However, As pointed by the user Martin Dawson in the comment below, This is not always ideal.
So whats the solution then?
Many
You can create a function to generate unique keys/ids/numbers/strings and use that
You can make use of existing npm packages like uuid, uniqid, etc
You can also generate random number like new Date().getTime(); and prefix it with something from the item you're iterating to guarantee its uniqueness
Lastly, I recommend using the unique ID you get from the database, If you get it.
Example:
const generateKey = (pre) => {
return `${ pre }_${ new Date().getTime() }`;
}
const savedLists = this.state.savedLists.map( list => {
const list_data = list.data.map( data => <li key={ generateKey(data) }>{ data }</li> );
return(
<div key={ generateKey(list.name) }>
<h2>{ list.name }</h2>
<ul>
{ list_data }
</ul>
</div>
)
});
It is important to remember that React expects STABLE keys, meaning you should assign the keys once and every item on your list should receive the same key every time, that way React can optimize around your data changes when it is reconciling the virtual DOM and decides which components need to re-render.
So, if you are using UUID you need to do it at the data level, not at the UI level.
Also keep in mind you can use any string you want for the key, so you can often combine several fields into one unique ID, something like ${username}_${timestamp} can be a fine unique key for a line in a chat, for example.
Keys helps React identify which items have changed/added/removed and should be given to the elements inside the array to give the elements a stable identity.
With that in mind, there are basically three different strategies as described bellow:
Static Elements (when you don't need to keep html state (focus, cursor position, etc)
Editable and sortable elements
Editable but not sortable elements
As React Documentation explains, we need to give stable identity to the elements and because of that, carefully choose the strategy that best suits your needs:
STATIC ELEMENTS
As we can see also in React Documentation, is not recommended the use of index for keys "if the order of items may change. This can negatively impact performance and may cause issues with component state".
In case of static elements like tables, lists, etc, I recommend using a tool called shortid.
1) Install the package using NPM/YARN:
npm install shortid --save
2) Import in the class file you want to use it:
import shortid from 'shortid';
2) The command to generate a new id is shortid.generate().
3) Example:
renderDropdownItems = (): React.ReactNode => {
const { data, isDisabled } = this.props;
const { selectedValue } = this.state;
const dropdownItems: Array<React.ReactNode> = [];
if (data) {
data.forEach(item => {
dropdownItems.push(
<option value={item.value} key={shortid.generate()}>
{item.text}
</option>
);
});
}
return (
<select
value={selectedValue}
onChange={this.onSelectedItemChanged}
disabled={isDisabled}
>
{dropdownItems}
</select>
);
};
IMPORTANT: As React Virtual DOM relies on the key, with shortid every time the element is re-rendered a new key will be created and the element will loose it's html state like focus or cursor position. Consider this when deciding how the key will be generated as the strategy above can be useful only when you are building elements that won't have their values changed like lists or read only fields.
EDITABLE (sortable) FIELDS
If the element is sortable and you have a unique ID of the item, combine it with some extra string (in case you need to have the same information twice in a page). This is the most recommended scenario.
Example:
renderDropdownItems = (): React.ReactNode => {
const elementKey:string = 'ddownitem_';
const { data, isDisabled } = this.props;
const { selectedValue } = this.state;
const dropdownItems: Array<React.ReactNode> = [];
if (data) {
data.forEach(item => {
dropdownItems.push(
<option value={item.value} key={${elementKey}${item.id}}>
{item.text}
</option>
);
});
}
return (
<select
value={selectedValue}
onChange={this.onSelectedItemChanged}
disabled={isDisabled}
>
{dropdownItems}
</select>
);
};
EDITABLE (non sortable) FIELDS (e.g. INPUT ELEMENTS)
As a last resort, for editable (but non sortable) fields like input, you can use some the index with some starting text as element key cannot be duplicated.
Example:
renderDropdownItems = (): React.ReactNode => {
const elementKey:string = 'ddownitem_';
const { data, isDisabled } = this.props;
const { selectedValue } = this.state;
const dropdownItems: Array<React.ReactNode> = [];
if (data) {
data.forEach((item:any index:number) => {
dropdownItems.push(
<option value={item.value} key={${elementKey}${index}}>
{item.text}
</option>
);
});
}
return (
<select
value={selectedValue}
onChange={this.onSelectedItemChanged}
disabled={isDisabled}
>
{dropdownItems}
</select>
);
};
Hope this helps.
Do not use this return `${ pre }_${ new Date().getTime()}`;. It's better to have the array index instead of that because, even though it's not ideal, that way you will at least get some consistency among the list components, with the new Date function you will get constant inconsistency. That means every new iteration of the function will lead to a new truly unique key.
The unique key doesn't mean that it needs to be globally unique, it means that it needs to be unique in the context of the component, so it doesn't run useless re-renders all the time. You won't feel the problem associated with new Date initially, but you will feel it, for example, if you need to get back to the already rendered list and React starts getting all confused because it doesn't know which component changed and which didn't, resulting in memory leaks, because, you guessed it, according to your Date key, every component changed.
Now to my answer. Let's say you are rendering a list of YouTube videos. Use the video id (arqTu9Ay4Ig) as a unique ID. That way, if that ID doesn't change, the component will stay the same, but if it does, React will recognize that it's a new Video and change it accordingly.
It doesn't have to be that strict, the little more relaxed variant is to use the title, like Erez Hochman already pointed out, or a combination of the attributes of the component (title plus category), so you can tell React to check if they have changed or not.
edited some unimportant stuff
Let React Assign Keys To Children
You may leverage React.Children API:
const { Children } = React;
const DATA = [
'foo',
'bar',
'baz',
];
const MyComponent = () => (
<div>
{Children.toArray(DATA.map(data => <p>{data}</p>))}
</div>
);
ReactDOM.render(<MyComponent />,document.getElementById("root"));
<div id="root"></div>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.6.3/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/16.6.3/umd/react-dom.production.min.js"></script>
To add the latest solution for 2021...
I found that the project nanoid provides unique string ids that can be used as key while also being fast and very small.
After installing using npm install nanoid, use as follows:
import { nanoid } from 'nanoid';
// Have the id associated with the data.
const todos = [{id: nanoid(), text: 'first todo'}];
// Then later, it can be rendered using a stable id as the key.
const todoItems = todos.map((todo) =>
<li key={todo.id}>
{todo.text}
</li>
)
Another option is weak-key: https://www.npmjs.com/package/weak-key
import weakKey from "weak-key";
const obj1 = {a : 42};
const obj2 = {b : 123};
const obj3 = {a : 42};
console.log(weakKey(obj1)); // 'weak-key-1'
console.log(weakKey(obj2)); // 'weak-key-2'
console.log(weakKey(obj3)); // 'weak-key-3'
console.log(weakKey(obj1)); // 'weak-key-1'
For a simple array of text-strings; I'm trying one of the two ways:
1. encodeURI which is available on both; NodeJS and browser
const WithEncoder = () => {
const getKey = useCallback((str, idx) => encodeURI(`${str},${idx}`), [])
return (
<div>
{["foo", "bar"].map((str, idx) => (
<div key={getKey(str, idx)}>{str}</div>
))}
</div>
)
}
2. window.btoa which is available only in browser.
const WithB2A = () => {
const getKey = useCallback((str, idx) => window.btoa(`${str}-${idx}`), [])
return (
<div>
{["foo", "bar"].map((str, idx) => (
<div key={getKey(str, idx)}>{str}</div>
))}
</div>
)
}
Depends on the situation, choose a uniqueId creator is ok when you just want render silly items, but if you render items like drag&drop etc and you haven't any uniqueId for each item, I recommend remap that data in your redux, mapper, wherever and add for each item an uniqueId (and not in the render like <Item key={...}) because React couldn't perform any check between renders (and with that all the benefits).
With that remapped that you can use that new Id in your Component.
Here is what I have done, it works for reordering, adding, editing and deleting. Once set the key is not changed, so no unnecessary re-render. One PROBLEM which may be a show stopper for some: it requires adding a property to your object at first render say "_reactKey".
Example for functional component in psuedo TS (ie it won't run in snippets):
interface IRow{
myData: string,
_reactKey?:number
}
export default function List(props: {
rows: Array<IRow>
}) {
const {myRows} = props;
const [nextKey, setNextKey] = useState(100);
const [rows, setRows] = useState<Array<IRow>|undefined>();
useEffect(function () {
if (myRows) {
for (let row of myRows){
if (!row._reactKey){
row._reactKey = nextKey;
setNextKey(nextKey+1);
}
}
setRows(myRows);
} else if (!rows) {
setRows([]);
}
}, [myRows, columns]);
addRow(){
let newRow = { blah, blah, _reactKey : nextKey};
setNextKey(nextKey+1);
rows.push(newRow);
setRows({...rows});
}
function MyRow(props:{row:IRow}){
const {row} = props;
return <tr><td>{row._reactKey}</td><td>row.myData</td></tr>
}
return <table>
<tr><th>Index</th><th>React Key</th><th>My Data</th></tr>
rows.map((row, key)=>{
return <MyRow key={row._reactKey} row={row} />
}
</table>
}
I don't use react too much, but the last time I saw this issue I just created a new state array, and tracked the keys there.
const [keys, setKeys] = useState([0]);
const [items, setItems] = useState([value: "", key: 0,])
Then when I add a new item to list, I get the last key from the keys array, add 1, then use setKeys to update the keys array. Something like this:
const addItemWithKey = () => {
// create a new array from the state variable
let newKeyArr = [...keys];
// create a new array from the state variable that needs to be tracked with keys
let newItemArr = [...items];
// get the last key value and add 1
let key = newKeyArr[newKeyArr.length-1] + 1;
newKeyArr.push(key);
newItemArr.push({value: "", key: key,});
// set the state variable
setKeys(newKeyArr);
setItems(newItemArr);
};
I don't worry about removing values from the keys array because it's only being used for iterating in the component, and we're trying to solve for the case where we remove an item from the list and/or add a new item. By getting the last number from the keys array and adding one, we should always have unique keys.
import React, {useState} from 'react';
import {SafeAreaView,ScrollView,StyleSheet,Text,View,Dimensions} from 'react-native';
const {width}=Dimensions.get('window');
function sayfalar(){
let pages=[]
for (let i = 0; i < 100; i++) {
pages.push(<View key={i} style={styles.pages}><Text>{i}</Text></View>)
}
return pages
}
const App=()=>{
return(
<View style={styles.container}>
<ScrollView horizontal={true} pagingEnabled={true}>
{sayfalar()}
</ScrollView>
</View>
)
}
const styles = StyleSheet.create({
container:{
flexDirection:'row',
flex:1
},
pages:{
width:width
}
})
export default App;
Use the mapped index (i)
things.map((x,i) => {
<div key=i></div>
});
Hope this helps.
You can use react-html-id to generate uniq id easely : https://www.npmjs.com/package/react-html-id
The fastest solution in 2021 is to use uniqid: Go to https://www.npmjs.com/package/uniqid for more info but to sum up:
First in your terminal and your project file: npm install uniqid
Import uniqid in your project
Use it in any key that you need!
uniqid = require('uniqid');
return(
<div>
<div key={ uniqid() } id={list.name}>
<h2 key={ uniqid() }>{list.name}</h2>
<ListForm update={lst.updateSaved} name={list.name}/>
</div>
</div>
)
});
I am using this:
<div key={+new Date() + Math.random()}>
I have list of data getting fetched from the API and each index in data is creating a <div> which consist of some information and button along with it.
Now when I click on button, a textarea and submit button should open for that <div> and closes when clicked again.
I tried to create this here.
To achieve this, I am creating n number of states and update the state when user click the button.
How can I achieve this and where am I going wrong ?
This is a working example of what you're looking for:
const { useState } = React;
const Counter = () => {
const [count, setCount] = useState(0);
const data = [
{"id":100},
{"id":200},
{"id":300},
{"id":400},
];
const [show,setShow] = useState([]);
const handleClick = id => e => {
const showCopy = [...show];
if(show[id]){
showCopy[id] = false;
} else {
showCopy[id] = true;
}
setShow(showCopy);
}
return (
<div>
{
data.map((k,v) => (
<div key={v}>
<div>
<p>Data{v+1}</p>
<p>Some More Information</p>
</div>
<button onClick={handleClick(v)}>Update</button>
<br/>
{
show[v] ? <div>
<textarea></textarea>
<button id={v}>Delete</button>
</div> : <></>
}
<hr/>
</div>
))
}
</div>
)
}
ReactDOM.render(<Counter />, document.getElementById('app'))
A couple things were wrong in your sample code:
Improper use of dot operators instead of brace operators
The JS dot (.) operator is used to access named attributes associated with the given JS object. In these particular cases, the values v and id are dynamic, and not the true names of the attributes desired. Using the brace [] operators allows you to access the dynamic value stored in the variable.
Improper array state update
In your example, the code you had written was creating a new array based on the contents of the previous array and adding a new object every time with a literal attribute named id. In the updated code, a copy of the original state array is created and the desired boolean value with index id is modified.
i have this code https://stackblitz.com/edit/react-wc2ons?file=src%2FSection.js
I have sections, and i can add items to those sections. How can i delete some item? I tried
const removeItem = (i) => {
setSections((section) => {
const itemTarget = section.items[i];
const filtered = section.items.filter((item) => item !== itemTarget);
return {
...section,
items: filtered,
};
});
};
But for some reason it doesn't work
The removeItem callback prop you pass into the Section component is the way to go and you should get rid of passing setSections down to it as well.
removeItem={(i) => removeItem(index, i)}
Child components shouldn't do parent's work so you had it right at first, I'm going to help you implement that since I can already see the removeItem handler being there in the App component.
removeItem has already all the info you need, I'm going to rename the arguments so it's more clear.
const removeItem = (sectionIndex, index) => {
const newSections = sections.slice();
const newItems = newSections[sectionIndex].items.slice();
newItems.splice(index, 1);
newSections[sectionIndex].items = newItems;
setSections(newSections);
};
Then get rid of removeItem implementation in the Section component and destructure it from the props.
You are using setSections, but you return a single section instead of an array of sections. You probably need something like this:
// using the `section` variable from the upper scope
const removeItem = (i) => {
setSections((sections) => {
const itemTarget = section.items[i];
const filtered = section.items.filter((item) => item !== itemTarget);
const newSections = [...sections];
newSections[section.id] = {
...section,
items: filtered,
};
return newSections;
});
};
A few tips (you don't have to follow them): TypeScript can prevent such mistakes and give useful error messages. Immer.js can make writing such code simpler.
Your problem is that section is an array. So you are currently accessing the undefined property items on it. You would have to change your function to something like this
const removeItem = (i) => {
setSections((section) /* aqui vc tinha chamado de prev*/ => {
const itemTarget = section[i].items[j];
const filtered = section[i].items.filter((item) => item !== itemTarget);
return [...section, {
...section[i],
items: filtered,
}]
});
};
where i is the section in question and j is the item you want to delete.
here is a crude solution to your problem (i noticed other bugs in the code but this solves your issue with removing items at least), but i would separate the sections and items into separate components that in turn has its own states.
There you can add/remove items withing its parent section much more easily.
Now we have to work around this by looking for which section the code wants to remove the current item in.
https://stackblitz.com/edit/react-xxbvp1?file=src%2FSection.js
So I am new to javascript and I tried making a todo list. This works well with adding elements. The issue is when I am removing some item, the first one gets removed too, why is it so? I know I am missing a small thing and this may be really basic but I am not able to find out what that is.
const App1 = () => {
const [item, updatedItem]=useState('');
const [Items, setItems]=useState([]);
function inputEvent(event) {
updatedItem(event.target.value);
}
const addItem = (event) => {
event.preventDefault();
setItems((prev) => {
return[
...prev,
item
]
});
updatedItem('');
}
let key=0;
return(<>
<div className='back'>
<div className='list'>
<header>ToDo List</header>
<form onSubmit={addItem}>
<input type='text' placeholder='Add an item' value={item} onChange={inputEvent}/>
<button type='submit'>+</button>
</form>
<div className='items'>
<ol>
{Items.map((val) => <li><button id={key++} onClick={(event) => {
setItems((Items) => {
return Items.filter((val, index) => {
if(index!==Number(event.target.id)){
return index;
}
}
);
});
key=0;
}}>x</button>{val}</li>)}
</ol>
</div>
</div>
</div>
</>);
You return the index in your filter, expecting this to always be true, yet 0 (the index of the first element) is a falsy value.
Try this instead:
return Items.filter((_val, index) => index !== Number(event.target.id));
Some unrelated code-quality notes:
In React, you should always set a key prop on each element when looping through them, rather than id.
map has a second argument, index, which it passes into the callback --- you don't have to keep track of this yourself with e.g. key++ etc.
If you use map's index parameter, then you can pass that directly into your filter rather than using Number(event.target.id), which is not very idiomatic in React.
If you don't use an argument of a callback, it's a good idea to prefix it with a _ (like I've done with _val here), to make it explicit that you're not using it.
Your filter callback should return a flag. index is a number. When treated as a flag, 0 is false (more on MDN). Instead:
return Items.filter((val, index) => index !== Number(event.target.id));
However, your code is returning an array of li elements without setting key on them (see: keys), which React needs in order to manage that list properly (you should be seeing a warning about it in devtools if you're using the development version of the libs, which is best in development). You can't use the mechanism you're using now for keys when doing that, it will not work reliably (see this article linked by the React documentation). Instead, assign each Todo item a unique ID when you create it that doesn't change, and use that as the key (and as the value to look for when removing the item):
// Outside the component:
let lastId = 0;
// Inside the component:
const addItem = (event) => {
event.preventDefault();
setItems((prev) => {
return [
...prev,
{text: item, id: ++lastId}
];
});
updatedItem("");
};
// Add a remove function:
const removeItem = ({currentTarget}) => {
const id = +currentTarget.getAttribute("data-id"); // Get the ID, convert string to number
setItems(items => items.filter(item => item.id !== id));
};
// When rendering:
{Items.map((item) => <li key={item.id}><button data-id={item.id} onClick={removeItem}>x</button>{item.text}</li>)}
In some cases it may be useful to use useCallback to memoize removeItem to avoid unnecessary rendering, but often that's overkill.
So, I've got a bit of a doozy here. I've looked into trees and the like in react, and I'm fairly confident I can implement one, given the right data structure. The problem I'm running into is that I'm getting my data from an API that doesn't, at least natively, have the structure for a tree, so I'm trying to create that structure on the fly.
This is what the data I'm getting back from the API looks like:
const category = //could have children
{
"object_name":"B2B",
"data_provider_key":"bluekai",
"object_key": "bluekai-31",
"object_type":"category",
};
const segment = //will only be a child
{
"object_name":"B2B > Role/Title > Admin Exec",
"data_provider_key":"bluekai",
"object_key": "bluekai-1145",
"object_type":"segment",
"cpm_cost":2.500
};
And this is the logic that I'm using to try and manipulate the data from the API to add children/create parents, etc.
const asyncView = async function (segTree: string | undefined) {
const categoryDataCall = api.getBeeswaxSegmentView(categoryBody);
const segmentDataCall = api.getBeeswaxSegmentView(segmentBody);
const data = await Promise.all([categoryDataCall, segmentDataCall]);
const parent = categoryData.find( (el: any) => el.object_key === segTree);
const categories = data[0].payload;
if (categories.length >= 1) {
for (let i = 0; i < categories.length; i++) {
categories[i].children = [];
}
}
parent.children = categories.concat(data[1].payload);
setCategoryData(parent.children);
setParent(parent);
}
asyncView(e.currentTarget.dataset.segment_tree);
}
return (
<>
<div>PARENT: {parent.object_name}</div>
{categoryData.length === 0
? <div>No category data</div>
: categoryData.map((e: any) => {
if (e.object_type === 'segment') {
return (
<div data-segment_tree={`${e.object_key || "NULL"}`}
data-provider_key={`${e.data_provider_key}`}
>
{`Name: ${e.object_name} (${e.object_key}, $${parseFloat(e.cpm_cost).toFixed(2)} CPM)`}
</div>
)
}
return (
<div data-segment_tree={`${e.object_key || "NULL"}`}
data-provider_key={`${e.data_provider_key}`}
onClick={getCategoryAndSegmentData}
>
{`Name: ${e.data_provider_name || e.object_name}`}
</div>
)
})
}
</>
);
}
I haven't implemented the Tree part yet, but that's because I am fairly confident I'm not creating the relations between elements correctly in my logic/the logic breaks if there are multiple 'trees'/categories on a page (which there will be.)
Sorry if this is a bit much, but any help or just ideas on dynamically modifying the data from the API to fit the tree structure of child/parent relationships would be appreciated!
Edit in response to Ray Hatfield:
What's the relationship between a category and a segment?
Segments will always be children of Categories, and will never have children of their own. Categories can have other categories as children.
How do you establish which category a segment belongs to?
The object_key property from the Category object gets passed to the API call(s) (two calls are made: one for segments, and one for categories). This is the only relation between segments and categories - nothing else in the return data ties them together.
What is e?
I assume you mean in the e.currentTarget.dataset.segment_tree line.
e is the event object, which I'm using to create the queries and firing them off on click events. I'm storing the object_key in a data-attribute in the HTML, and then passing it to a handler to generate the categoryBody and segmentBody used in the asyncView() function.
For some reason I have to explicitly pass the e.currentTarget.dataset.segment_tree as an argument to the async function even though they're in the same scope, but all it's doing is allowing me to find the Category that was clicked in the existing array of data in state.
What is categoryData?
categoryData is the array of values ( that is currently in state. So, each time I hit the API I update category data to re-render everything.
Effectively, I'm finding the parent (category that was clicked) firing off the API calls to get all the subcategories/segments associated with the clicked categories object_key, and then adding a children prop to any incoming categories, and then setting the children of the last clicked element equal to the returned segments + categories, and then rendering.
I put together this working demo on jsfiddle. Here are the highlights:
The Core Idea
The core idea is a Category component that's responsible for loading and rendering its own segments and subcategories. The subcategories get rendered using the same Category component, resulting in a recursive tree structure.
The Category Component
const Category = ({item}) => {
const [data, setData] = React.useState();
const onClick = data
? () => setData(null) // discard data (collapse) on subsequent click
: () => load(item.object_key).then(setData);
return (
<div className="category">
<div
className={`category-name ${data ? 'open' : ''}`}
onClick={onClick}
>
{item.object_name}
</div>
{data && (
<ul>
{ data.map((child, i) => (
<li key={i}><Node item={child}/></li>
))}
</ul>
)}
</div>
)
}
This component takes a single item prop representing the category. The component expects item to have object_key and object_name fields, like the category object in your example.
Initially the component has no information other than what's in the item, so it renders the category's name with an onClick handler that makes API calls to fetch the category's children and then stores the result in the component's state:
const [data, setData] = React.useState();
const onClick = () => load(item.object_key).then(setData);
On the subsequent render the Category component renders its children (segments and subcategories) in addition to the category name. Subcategories are rendered using the same Category component, resulting in a recursive tree structure.
The Segment Component
const Segment = ({item: {object_name}}) => (
<div className="segment">{object_name}</div>
);
Simple component for rendering segments. Just returns the segment name here, but you could of course expand it to do whatever you need it to do.
The Node Component
const Node = ({item}) => {
const Cmp = item.object_type === 'category' ? Category : Segment;
return <Cmp item={item} />;
};
Convenience component for rendering a <Segment /> or <Category /> for the given item according to its type.
The rest of the example code is just hand waving to simulate the API calls and generate mock data.
load function
const load = async (parentKey) => {
const [categories, segments] = await Promise.all([
mockApiRequest('category'),
mockApiRequest('segment')
]);
return [
...categories,
...segments
];
}
Given a category's object_key, this makes the api calls to get the segments and subcategories, merges and returns the results as a single array.
mockApiRequest
const mockApiRequest = (type) => (
new Promise((resolve) => {
setTimeout(() => resolve(fakeData(type)), 200);
})
)
Simulates the API request. Waits 200ms before resolving with mock data.
fakeData
// generate mock response data
const fakeData = (type) => {
// copy the list of names
const n = [...names];
// plucks a random name from the list
const getName = () => (
n.splice(Math.floor(Math.random() * n.length), 1)[0]
);
// generate and return an array of data
return Array.from(
{length: Math.floor(Math.random() * 5) + 1},
(_, i) => ({
...samples[type],
object_name: getName()
})
)
};
Generates mock category or segment data by copying the sample and choosing a random name.