How we will render an Array of Objects?We will use the map function to access each object from the array.The map() method in JavaScript creates an array by calling a specific function on each element present in the parent array. It is a non-mutating method. Generally, map() method is used to iterate over an array and calling function on every element of the array.Syntax: Return Value: It returns a new array and elements of arrays are the result of callback function. Example 1: In this example, we will simply create an array of objects that contains states and their capitals. We will render them in an unordered list. States are in red and bold.
const params: CutOffObject = {
cutOff: cutOff,
etd: etd,
pivotWt: pivotWt,
maxGw: maxGw,
minCbm: minCbm,
maxCbm: maxCbm,
flightNo: flightNo,
minGw: minGw,
}React.js is a declarative, efficient, and flexible JavaScript library for building user interfaces. It’s ‘V’ in MVC. ReactJS is an open-source, component-based front-end library responsible only for the view layer of the application. It is maintained by Facebook.
In this article, we will learn about How to render an array of objects in React.
Initially, we will begin with learning what is an array of objects.
Array of objects: It stores multiple values in a single variable. The object can contain anything in the real world, such as person names, cars, game characters. Objects are very easy to use in some situations, if you know where the data is being processed. The character set of objects are known as Properties. Properties of an object can be called by using DOT(“.”) notation and (“[]”) notation.
Syntax:
var object = [{
"property1": "value1",
"property2": "value2"
}]Now, let’s create a React application to learn How to render an array of objects.
Creating React Application:
Step 1: Create a React application using the following command.
npx create - react - app foldername
array.map(function(currentValue, index, arr), thisValue)import React from 'react'
function RenderingArrayOfObjects() {
const data = [
{
"State": "Uttar Pradesh",
"Capital": "Lucknow"
},
{
"State": "Gujarat",
"Capital": "Gandhinagar"
},
{
"State": "Karnataka",
"Capital": "Bengaluru"
},
{
"State": "Punjab",
"Capital": "Chandigarh"
},
{
"State": "Maharashtra",
"Capital": "Mumbai"
}
]
const listItems = data.map(
(element) => {
return (
<ul type="disc">
<li style={{
fontWeight: 'bold',
color: 'red' }}
>
{element.State}
</li>
<li>{element.Capital}</li>
</ul>
)
}
)
return (
<div>
{listItems}
</div>
)
}
function App() {
return (
<div className="App">
<div>
<h1 style={{ color: 'green' }}>
Pretagcode
</h1>
<h3>Rendering Array of Objects</h3>
<br></br>
<RenderingArrayOfObjects />
</div>
</div>
);
}
export default App;
You can do it in two ways: Important : Decision to use which value should we pass to key prop also matters as common way is to use index parameter provided by .map(). Stack Overflow for Teams is moving to its own domain! When the migration is complete, you will access your Teams at stackoverflowteams.com, and they will no longer appear in the left sidebar on stackoverflow.com. QGIS Expression: Finding DEM value at point where two lines on different layers intersect
First:
render() {
const data =[{"name":"test1"},{"name":"test2"}];
const listItems = data.map((d) => <li key={d.name}>{d.name}</li>);
return (
<div>
{listItems }
</div>
);
}
Second: Directly write the map function in the return
render() {
const data =[{"name":"test1"},{"name":"test2"}];
return (
<div>
{data.map(function(d, idx){
return (<li key={idx}>{d.name}</li>)
})}
</div>
);
}
You can pass any JavaScript expression as children, by enclosing it within {}. For example, these expressions are equivalent:
<MyComponent>foo</MyComponent>
<MyComponent>{'foo'}</MyComponent>
class First extends React.Component {
constructor(props) {
super(props);
this.state = {
data: [{name: 'bob'}, {name: 'chris'}],
};
}
render() {
return (
<ul>
{this.state.data.map(d => <li key={d.name}>{d.name}</li>)}
</ul>
);
}
}
ReactDOM.render(
<First />,
document.getElementById('root')
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="root"></div>The Array.map() method is key to rendering objects and data in react and it is a prototype function on all arrays in JavaScript. This means you can call it on any array with the following syntax: [].map(callback). This syntax is on any array in JavaScript. When you call .map() you are going to need to provide a callback function for the method to be able to use. When we call the Array.map() function in JavaScript it will transform the array into whatever we return from the callback function we pass into it.
const arrayOfObjects = [
{ coffee: "Americano", size: "Medium" },
{ coffee: "Espresso", size: "Single" },
];
export default function MyReactComponent() {
return (
<>
{arrayOfObjects.map(({ coffee, size }) => (
<p key={coffee}>Coffee type {coffee} in a {size} size.</p>
))}
</>
);
}[1, 2, 3].map((arrayItem, arrayItemIndex, wholeArray) => {
arrayItem; // 1
arrayItemIndex; // 0
wholeArray; // [1, 2, 3]
});[1, 2]; // [1, 2]
[1, 2].map(n => n * 10); // [10, 20]
[1, 2].map(n => `Hello World ${n}`); // [‘Hello World 1', ‘Hello World 2']arrayOfObjects.map(
({
coffee,
size
}) => `Coffee type ${coffee} in a ${size} size.`
);const arrayOfObjects = [
{ coffee: "Americano", size: "Medium" },
{ coffee: "Espresso", size: "Single" },
];
export default function MyReactComponent() {
return (
<p>
{arrayOfObjects.map(
({ coffee, size }) => `Coffee type ${coffee} in a ${size} size.`
).join(' ')}
</p>
);
}Below, you loop through the reptiles array and return a li element for each item in the array. You can use this method when you want to display a single element for each item in the array: In this step, you will render multiple elements in a component and add a unique key. Update the code to include a key on the list items to resolve the warning: When rendering an element inside another component, you should use a unique key and wrap your elements inside a wrapper element. In JSX, to render more than one element in a component you must add a wrapper around them.
To render multiple JSX elements in React, you can loop through an array with the .map() method and return a single element.
function ReptileListItems() {
const reptiles = ["alligator", "snake", "lizard"];
return reptiles.map((reptile) => <li>{reptile}</li>);
}
The output will look like this:
Output - alligator - snake - lizard
In this example, you loop through an array and create a series of list item components like the previous example.
To start, update the code to use the <ol> component to hold the <li> items. The <ol> component will create an ordered list of the items:
function ReptileList() {
const reptiles = ["alligator", "snake", "lizard"];
return (
<ol>
{reptiles.map((reptile) => (
<li>{reptile}</li>
))}
</ol>
);
}
In JSX, to render more than one element in a component you must add a wrapper around them.
In this example, you will first return a list of items without looping through an array:
function ReptileListItems() {
return (
<li>alligator</li>
<li>snake</li>
<li>lizard</li>
);
}
To fix this error you need to wrap the block of li elements in a wrapper. For a list you can wrap them in an ol or ul element:
function ReptileListItems() {
return (
<ol>
<li>alligator</li>
<li>snake</li>
<li>lizard</li>
</ol>
);
}
Call the find() method on the array, passing it a function. Use the filter() method to find multiple objects that satisfy a condition in an array in React. The filter method takes a function as a parameter and returns an array containing only the elements that satisfy the condition. The function we passed to the Array.find method gets called with each element (object) in the array until it returns a truthy value or iterates over the entire array. The function should return an equality check on the relevant property.
Copied!const App = () => {
const arr = [
{id: 1, country: 'Austria'},
{id: 2, country: 'Germany'},
{id: 3, country: 'Austria'},
];
// ✅ Find first object that matches condition
const found = arr.find(obj => {
return obj.id === 1;
});
// 👇️ {id: 1, country: 'Austria'}
console.log(found);
// -----------------------
// ✅ Find multiple objects that satisfy condition
const filtered = arr.filter(obj => {
return obj.country === 'Austria';
});
// 👇️ [{id: 1, country: 'Austria'}, {id: 3, country: 'Austria'}]
console.log(filtered);
return (
<div>
{/* 👇️ render single object */}
{found && (
<div>
<h2>id: {found.id}</h2>
<h2>country: {found.country}</h2>
</div>
)}
<hr />
{/* 👇️ render array of objects */}
{filtered.map(obj => {
return (
<div key={obj.id}>
<h2>id: {obj.id}</h2>
<h2>country: {obj.country}</h2>
</div>
);
})}
</div>
);
};
export default App;
Copied!
const arr = [{
id: 1,
country: 'Austria'
},
{
id: 2,
country: 'Germany'
},
{
id: 3,
country: 'Austria'
},
];
const notFound = arr.find(obj => {
return obj.id === 123;
});
console.log(notFound); // 👉️ undefinedCopied!const App = () => {
const arr = [
{id: 1, country: 'Austria'},
{id: 2, country: 'Germany'},
{id: 3, country: 'Austria'},
];
// ✅ Find multiple objects that satisfy condition
const filtered = arr.filter(obj => {
return obj.country === 'Austria';
});
// 👇️ [{id: 1, country: 'Austria'}, {id: 3, country: 'Austria'}]
console.log(filtered);
return (
<div>
{/* 👇️ render array of objects */}
{filtered.map(obj => {
return (
<div key={obj.id}>
<h2>id: {obj.id}</h2>
<h2>country: {obj.country}</h2>
</div>
);
})}
</div>
);
};
export default App;
You’ve learned how to conveniently render an array of objects in React with the help of the map() method. From this time forward, you can build more complex things with this technique in mind. If you’d like to explore more new and exciting stuff about modern React, take a look at the following articles: In React, the most popular way to render an array of objects is to use the Array.map() method. This method calls a function once for each element in the array: The complete example below will give you a better understanding of how to apply this in action.
<div>
{items.map((item) =>
<div key={item.id}>{/* ... */}</div>
)}
</div>This sample app displays a list of employees of a fiction company. The array that holds the data looks like this:
const employees = [{
id: 'e1',
name: 'Person One',
salary: 5000
},
/* ... */
]The complete source code in src/App.js with explanations:
// KindaCode.com
// src/App.js
// Dummy data for the app
const employees = [
{
id: 'e1',
name: 'Person One',
salary: 5000
},
{
id: 'e2',
name: 'Person Two',
salary: 6000
},
{
id: 'e3',
name: 'Person Three',
salary: 4500
},
{
id: 'e4',
name: 'Person Four',
salary: 7000
},
{
id: 'kindacode.com',
name: 'Person Five',
salary: 8000
}
]
function App() {
return (
<div style={styles.container}>
<h1>Employee List</h1>
{/* Render the list */}
<div>
{employees.map((employee) =>
<div key={employee.id} style={styles.listItem}>
<h3>{employee.name}</h3>
<p>Salary: {employee.salary}</p>
</div>)
}
</div>
</div>
);
}
// Styling
const styles = {
container: {
backgroundColor: '#fff9c4',
padding: '10px 50px 60px 50px'
},
listItem: {
borderTop: '1px dashed #ccc'
}
}
export default App;And that's it. You've successfully studied the art of state management with objects and arrays. Tackling state-related issues should now be a breeze for you. If you'd like to chat more about this topic, ping me on Twitter @DesmondNyamador. If you're integrating your React app with an API, you probably would like to store values obtained from the API call in an array in state without losing previous values the array contained. The spread operator helps you do that easily. Take a close look at the snippet below, which implements the spread operator in finalArray by "spreading" the contents of oldArray. With the introduction of hooks in React 16.8, functional components can now also handle state in a simplified way. The snippet below is the class-based <MyComponent/> written as a functional component. The useState hook is a function that takes in a default value as a parameter (which can be empty) and returns an array containing the state and a function to update it. Array destructuring is used to extract the values from the result of the useState function call.
1import React from 'react'
2
3class MyComponent extends React.Component {
4 constructor(props){
5 super(props);
6 this.state = { date: new Date(), name: 'Kofi'};
7 }
8
9 render(){
10 return(
11 <div>
12 <p> Hello {this.state.name} , it is {this.state.toLocaleTimeString()
13 <p>Date: {this.state.date.toLocaleDateString()}
14 </div>
15 )
16 }
17}1import React, {useState} from 'react';
2
3function MyComponent(){
4
5 const [date, setDate] = useState(new Date())
6 const [name, setName] = useState("Kofi");
7
8 return(
9 <div>
10 <p> Hello {date.name} , it is {date.toLocaleTimeString()
11 <p>Date: {date.toLocaleDateString()}
12 <button onClick={setDate(new Date())}></button>
13 </div>
14 )
15}1
const oldArray = ['peter piper', 'picked a pair']
2
3
const finalArray = [...oldArray, 'of pickle pepper']
4
5 console.log(finalArray)
6
7 // (3) ["peter piper", "picked a pair", "of pickle pepper"]1import React, { useState, useEffect } from 'react';
2
3const ProductsPage = () => {
4 const [productsList, setProductsList] = useState([]);
5 const [isLoading, setisLoading] = useState(true);
6
7 useEffect(() => {
8 fetch('http://127.0.0.1:8000/api/v1/products/all')
9 .then((res) => res.json())
10 .then((data) => setProductsList({...data}))
11 .then(setisLoading(false));
12 }, []);
13
14 return (
15 <>
16 <Header />
17 {isLoading ? (
18 <div className='spinner-border text-primary' role='status'>
19 {' '}
20 <span className='sr-only'>Loading...</span>{' '}
21 </div>
22 ) : (
23 Object.keys(productList).map(product => {
24 <p key={productList[product].id}>{productList[product].name}</p>
25 })
26 )}
27 </>
28 );
29};
30
31}You can build collections of elements and include them in JSX using curly braces {}. Below, we loop through the numbers array using the JavaScript map() function. We return a <li> element for each item. Finally, we assign the resulting array of elements to listItems: JSX allows embedding any expression in curly braces so we could inline the map() result: Given the code below, we use the map() function to take an array of numbers and double their values. We assign the new array returned by map() to the variable doubled and log it:
const numbers = [1, 2, 3, 4, 5];
const doubled = numbers.map((number) => number * 2);
console.log(doubled);const numbers = [1, 2, 3, 4, 5];
const listItems = numbers.map((number) => <li>{number}</li>);<ul>{listItems}</ul>function NumberList(props) {
const numbers = props.numbers;
const listItems = numbers.map((number) =>
<li key={number.toString()}> {number}
</li>
);
return (
<ul>{listItems}</ul>
);
}const numbers = [1, 2, 3, 4, 5];
const listItems = numbers.map((number) =>
<li key={number.toString()}> {number}
</li>
);On each iteration, call the map() method on the nested array. map method gets called with each element in the array and the index of the current iteration.To render a nested array using map(): Use the map() method to iterate over the outer array. To map or iterate an array of objects in react native, just use the map() method it will work like foreach loop and you can easily write components in it. Like the following example, we can iterate an array of objects using the map() method.24-Jun-2022
In this lesson, we'll use programming to try to solve the React Native Render Array Of Objects puzzle. The code shown below demonstrates this.
render() {
const data =[{"name":"test1"},{"name":"test2"}];
return (
<div>
{data.map(function(d, idx){
return (<li key={idx}>{d.name}</li>)
})}
</div>
);
}
Below, you'll find some examples of different ways to solve the React Native Render Array Of Objects problem.
render() {
2
const data =[{"name":"test1"},{"name":"test2"}];
3
return (
4
<div>
5
{data.map(function(d, idx){
6
return (<li key={idx}>{d.name}</li>)
7
})}
8
</div>
9
);
10
}