React map array typescript

Display Array Data through map in react Typescript

In this tutorial, you’ll look at four noteworthy uses of in JavaScript: calling a function of array elements, converting strings to arrays, rendering lists in JavaScript libraries, and reformatting array objects. Also you can use shorthand method of arrow function, Introduction From the classic loop to the method, various techniques and methods are used to iterate through datasets in JavaScript.

Display Array Data through map in react Typescript

I try to display Array data but does not display the data on the React web page. AnyOne guide me where is my mistake and correct me. Please see the comment line //

API Response

< "data": [ < "id": 1, "name": "Pizza Hut", "address": "Dwarka Sector-14", "rating": "4.5", "email": "pizzhut@pizza.com" >, < "id": 2, "name": "Mc-Dondle", "address": "Dwarka Sector-15", "rating": "4.0", "email": "mcdondle@mcdon.com" >], "status": 200, "statusText": "OK", "headers": < "cache-control": "no-cache", "content-type": "application/json; charset=utf-8", "expires": "-1", "pragma": "no-cache" >, "config": < "url": "http://localhost:3030/restauranst", "method": "get", "headers": < "Accept": "application/json, text/plain, */*" >, "transformRequest": [ null ], "transformResponse": [ null ], "timeout": 0, "xsrfCookieName": "XSRF-TOKEN", "xsrfHeaderName": "X-XSRF-TOKEN", "maxContentLength": -1, "maxBodyLength": -1 >, "request": <> > 

Return from your map function as you are missing return. and loader also try to use through state. By default make isLoadding to false

this.state = < restoLists: null, isLoadding : false >; componentDidMount() < this.setState() axios .get("http://localhost:3030/restauranst") .then((response) => < this.setState(< restoLists: response.data, isLoading: false>) >).catch((error) => console.error(error)); > 

You are not returning anything inside the map.

 this.state.restoLists.map((: any) => < return > ; >); 

Also you can use shorthand method of arrow function,

 this.state.restoLists.map((: any) => > ); 

Display Array Data through map in react Typescript, I try to display Array data but does not display the data on the React web page. AnyOne guide me where is my mistake and correct me. Please see the comment line // /* eslint-disable */ import Reac Usage examplethis.state.restoLists.map((: any) => > );Feedback

How To Use .map() to Iterate Through Array Items in JavaScript

Introduction

From the classic for loop to the forEach() method, various techniques and methods are used to iterate through datasets in JavaScript. One of the most popular methods is the .map() method. .map() creates an array from calling a specific function on each item in the parent array. .map() is a non-mutating method that creates a new array, as opposed to mutating methods, which only make changes to the calling array.

This method can have many uses when working with arrays. In this tutorial, you’ll look at four noteworthy uses of .map() in JavaScript: calling a function of array elements, converting strings to arrays, rendering lists in JavaScript libraries, and reformatting array objects.

Prerequisites

This tutorial does not require any coding, but if you are interested in following along with the examples, you can either use the Node.js REPL or browser developer tools.

• To install Node.js locally, you can follow the steps at How to Install Node.js and Create a Local Development Environment.
• Chrome DevTools are available by downloading and installing the latest version of Google Chrome.

Step 1 — Calling a Function on Each Item in an Array

.map() accepts a callback function as one of its arguments, and an important parameter of that function is the current value of the item being processed by the function. This is a required parameter. With this parameter, you can modify each item in an array and return it as a modified member of your new array.

const sweetArray = [2, 3, 4, 5, 35] const sweeterArray = sweetArray.map(sweetItem =>  return sweetItem * 2 >) console.log(sweeterArray) 

This output is logged to the console:

This can be simplified further to make it cleaner with:

// create a function to use const makeSweeter = sweetItem => sweetItem * 2; // we have an array const sweetArray = [2, 3, 4, 5, 35]; // call the function we made. more readable const sweeterArray = sweetArray.map(makeSweeter); console.log(sweeterArray); 

The same output is logged to the console:

Having code like sweetArray.map(makeSweeter) makes your code a bit more readable.

Step 2 — Converting a String to an Array

.map() is known to belong to the array prototype. In this step you will use it to convert a string to an array. You are not developing the method to work for strings here. Rather, you will use the special .call() method.

Everything in JavaScript is an object, and methods are functions attached to these objects. .call() allows you to use the context of one object on another. Therefore, you would be copying the context of .map() in an array over to a string.

.call() can be passed arguments of the context to be used and parameters for the arguments of the original function.

const name = "Sammy" const map = Array.prototype.map const newName = map.call(name, eachLetter =>  return `$eachLetter>a` >) console.log(newName) 

This output is logged to the console:

Here, you used the context of .map() on a string and passed an argument of the function that .map() expects.

This works like the .split() method of a string, except that each individual string characters can be modified before being returned in an array.

Step 3 — Rendering Lists in JavaScript Libraries

JavaScript libraries like React use .map() to render items in a list. This requires JSX syntax, however, as the .map() method is wrapped in JSX syntax.

Here’s an example of a React component:

import React from "react"; import ReactDOM from "react-dom"; const names = ["whale", "squid", "turtle", "coral", "starfish"]; const NamesList = () => ( div> ul>names.map(name => li key=name>> name> /li>)>/ul> /div> ); const rootElement = document.getElementById("root"); ReactDOM.render(NamesList />, rootElement); 

This is a stateless component in React, which renders a div with a list. The individual list items are rendered using .map() to iterate over the names array. This component is rendered using ReactDOM on the DOM element with Id of root .

Step 4 — Reformatting Array Objects

.map() can be used to iterate through objects in an array and, in a similar fashion to traditional arrays, modify the content of each individual object and return a new array. This modification is done based on what is returned in the callback function.

const myUsers = [  name: 'shark', likes: 'ocean' >,  name: 'turtle', likes: 'pond' >,  name: 'otter', likes: 'fish biscuits' > ] const usersByLikes = myUsers.map(item =>  const container = >; container[item.name] = item.likes; container.age = item.name.length * 10; return container; >) console.log(usersByLikes); 

This output is logged to the console:

Here, you modified each object in the array using the bracket and dot notation. This use case can be employed to process or condense received data before being saved or parsed on a front-end application.

Conclusion

In this tutorial, we looked at four uses of the .map() method in JavaScript. In combination with other methods, the functionality of .map() can be extended. For more information, see our How To Use Array Methods in JavaScript: Iteration Methods article.

“With this parameter, you can modify each item in an array and create a new function.”

Shouldn’t this say “create a new array”? I don’t see how .map creates a “new function”.

Typescript array.map Code Example, Answers related to “typescript array.map” typescript array; arrays in typescript; react array props typescript type; typescript map list to new list of objects; typescript type from array; typescript initialize map inline; typescript key value array; typescript array of react elements; typescript hashmap; typescript key …

Using state in react with TypeScript

I am new to TypeScript. I’ve got a problem with displaying this.state.something inside the render method or assigning it to a variable inside a function.

Have a look at the most important piece of code:

interface State < playOrPause?: string; >class Player extends React.Component < constructor() < super(); this.state = < playOrPause: 'Play' >; > render() < return( 
 this.playPause = playPause> title= // in this line I get an error > Play 
 ); > > 

The errors says: «[ts] Property ‘playOrPause’ does not exist on type ‘ReadOnly>’.

I tried to declare the playOrPause property to be a type of string and it didn’t work. What am I missing here to make it work?

You need to declare that your component is using the State interface, it used by Typescript’s Generics.

interface IProps < >interface IState < playOrPause?: string; >class Player extends React.Component < // ------------------------------------------^ constructor(props: IProps) < super(props); this.state = < playOrPause: 'Play' >; > render() < return( 
 this.playPause = playPause> title= // in this line I get an error > Play 
 ); > > 

In case anyone is wondering how to implement it in functional components with hooks ( not in a class) :

const [value, setValue] = useState(0); 

useState is a generic function, that means that it can accept a type parameter. This type-parameter will tell TypeScript which types are acceptable for this state.

In my case ( working with TypeScript, and the state value was actually a boolean ) I’ve had the same problem, I’ve fixed it by passing the state value I wanted to mark as output to String():

import React, < Component >from 'react'; interface ITestProps < name: string; >interface ITestState < toggle: boolean; >class Test extends Component < constructor(props: ITestProps) < super(props); this.state = < toggle: false, >; this.onClick = this.onClick.bind(this); > onClick() < this.setState((previousState, props) =>(< toggle: !previousState.toggle, >)); > render() < return ( Hello, ! 
Toggle state is: ) > > 

Just declare interface or type with property, types, and annotate it to state. the ? mean optional:

interface ITestProps <> interface ITestState < playOrPause?: string; >class Player extends React.Component < state = < playOrPause: 'Play' >; render() < return // your code here >

You can add more value as per your need to interface above if then you need the same state to pass it to child component you just need to create a file with .d.ts and you should be good to go!

Array map in typescript Code Example, how to add an element to a Typescript array; state in react typescript; typescript format string; npx react-native init MyApp —template react-native-template-typescript not working; size of array typescript; typescript if then shorthand; typescript string to enum; react typescript pass component as prop; …

Источник

How to map array to another array in typescript example

This is easy and simple to populate an array from another array.

The first way is using the slice method of an array second, using Array. from method The third way is using spread operator

Here is an example, the output is the same across all methods

let roles = ["one", "two", "three"]; let sliceRoles = roles.slice(); let fromRoles = Array.from(roles); let newRoles = [. roles]; console.log(roles); console.log(sliceRoles); console.log(fromRoles); console.log(newRoles);

How to map an array of Objects to another array of Objects

There are many ways we can achieve

Array.map method

the map is a method in the array used to iterate each item in an array and transform it into a new item.

This method takes the input of n size and converts it into new output with the same size.

For example, We have an array of the user object Each user contains firstname, lastname, id, role

let users = [  id: "1", fname: "john", lname: "Ken", role: "admin", >,  id: "2", fname: "Eric", lname: "Dawn", role: "user", >,  id: "3", fname: "Andrew", lname: "Karvin", role: "admin", >, ];

if we want to convert to a new array with the user object Where each user object contains the name(firstname,lastname), id, and role

let newusers = users.map((user) =>  return  name: user.fname + " " + user.lname, id: user.id, role: user.role >; >); console.log(newusers);

The array has a map() method, iterates each element of an array and constructs a new object, and returns a new array. The new object is returned and assigned to newusers

[  name: "john Ken", id: "1", role: "admin", >,  name: "Eric Dawn", id: "2", role: "user", >,  name: "Andrew Karvin", id: "3", role: "admin", >, ];

forEach method in the typescript

• Declare an array of any type, initialize an object array data
• Declare a new result array of any type which is going to assign part of the original array.
• Iterate an array using the forEach loop
• add each item to a new result with the required fields
• Finally, a new array is returned

var books: Arrayany> = [  id: "1", rating: 5, name: "Book1", >,  id: "2", rating: 4, name: "Book", >,  id: "11", rating: 3, name: "Book3", >, ]; var bookRatings: Arrayany> = []; console.log(bookRatings); books.forEach((item) =>  bookRatings.push( name: item.name, rating: item.rating, >); >); console.log(bookRatings);

[  "name": "Book1", "rating": 5 >,  "name": "Book", "rating": 4 >,  "name": "Book3", "rating": 3 > ]

Lodash and Underscore _.map to populate another array object

Lodash and Underscore libraries have map method which behaves the same as like array method.

let result = Arrays.map(users, function transform(user)  return  name: user.fname + " " + user.lname, id: user.id, role: user.role >; >);

Conclusion

To Sum up, Learned how to map strings to an array of strings with examples.

Источник