type MyObject = {
  [key: string]: number;
const obj: MyObject = {
  a: 1,
  b: 2,
  c: 3
console.log(obj); 
Output:
{ a: 1, b: 2, c: 3 }
Using Interface
You can also use an interface to define your custom type where the keys of the object are typed to a specific type and can later be used to type the interface.
Interface interfaceName{}
Example: The below code example explains the use of the interface to declare specific type of keys in an object.

            JavaScript
    
interface MyObject {
    [key: string]: number;
const obj: MyObject = {
    a: 1,
    b: 2,
    c: 3
console.log(obj); 
Output:
{ a: 1, b: 2, c: 3 }
Using Inline Mapped Types with type
You can define a mapped type inline using the type keyword in TypeScript. This allows you to specify the keys of a particular type directly within the type declaration.
Syntax:
type TypeName = { [KeyType]: ValueType };
Example: This TypeScript code defines a type MyObject allowing string keys with number values. It creates an object obj with properties assigned numeric values and logs it.

            JavaScript
    
type MyObject = { [key: string]: number };
const obj: MyObject = {
    a: 1,
    b: 2,
    c: 3
console.log(obj);
Output:
{
  "a": 1,
  "b": 2,
  "c": 3
} 
Using Record Utility Type
TypeScript provides utility types that help in creating complex types from existing ones. These can be particularly useful for specifying specific key types in an object.
Example: The Record utility type is used to construct an object type with specified keys and a uniform value type.

            JavaScript
    
// Define a type with specific keys of a certain type
type MyObject = Record<'name' | 'age' | 'email', string>;
// Create an object conforming to the specified type
const obj: MyObject = {
    name: "Nikunj",
    age: "22",
    email: "[email protected]"
console.log(obj);

Output
{ name: 'Nikunj', age: '22', email: '[email protected]' }
In this article, we explored different methods to define specific key-value types in TypeScript using index signatures. We covered using mapped types, interfaces, and inline mapped types with the type keyword. Each method allows for flexible and robust object type definitions, ensuring type safety and consistency within your TypeScript code.
                
How to Declare Object Value Type Without Declaring Key Type in TypeScript ?
                
We will create an object value type without declaring the key type. We can not directly define the type of value we will use different methods for declaring the object value type. These are the following methods for declaring the object value type: Table of Content Using Record Utility TypeUsing Mapped TypesUsing GenericsBy utilizing Indexed TypesU
                
Typescript Record<Keys, Type> Utility Type
                
In this article, we are going to learn about the Record<Keys, Type> in Typescript. TypeScript is a programming language that is a strict syntactical superset of JavaScript. It adds optional static typing and class-based object-oriented programming to JavaScript, one of the features is Record<Keys, Type> which is a built-in utility type
                
TypeScript Pick<Type, Keys> Utility Type
                
TypeScript's Pick<Type, Keys> utility type allows you to create a new type by selecting specific properties (`Keys`) from an existing type (`Type`). This is useful for narrowing down types to only the relevant properties, enhancing type safety, and reducing redundancy in complex type definitions. Syntax type NewType = Pick<Type, Keys>;T
                
TypeScript Omit<Type, Keys> Utility Type
                
TypeScript's Omit<Type, Keys> utility type creates a new type by excluding specific properties (Keys) from an existing type (Type). It is useful for refining types by removing unnecessary properties, enhancing type safety, and simplifying complex type definitions in TypeScript applications. Syntax: type NewType = Omit<OriginalType, 'Key1'
                
How to Define Strongly Type Nested Object Keys with Generics in TypeScript ?
                
We will look into the effective use of generics in TypeScript to ensure type safety when working with nested objects. By employing generics, developers can establish strongly typed keys for nested objects, significantly reducing the likelihood of runtime errors and enhancing code maintainability. Table of Content Using Recursive GenericsUsing Condi
                
How to declare nullable type in TypeScript ?
                
In vanilla JavaScript, there are two primary data types: null and undefined. While TypeScript previously did not allow explicit naming of these types, you can now use them regardless of the type-checking mode. To assign undefined to any property, you need to turn off the --strictNullChecks flag. However, with this flag enabled, you cannot assign un
                
How to Filter Keys of Type string[] in TypeScript ?
                
In TypeScript, the filtering of keys of type string[] can be done by iterating over the data object, and applying the condition to the string if the key is a string. If the condition is satisfied, then an array of output results is created which consists of filtered keys of type string[]. The below methods can be used to filter the keys of type str
                
How to Create a Typed Array from an Object with Keys in TypeScript?




    

                
Creating a typed array from the keys of an object in TypeScript ensures that your application maintains type safety, particularly when interacting with object properties. Here we'll explore different approaches to achieve this using TypeScript's built-in Object methods. Below are the approaches used to create a Typed Array from an Object with Keys
                
How to Declare a Function that Throws an Error in TypeScript ?
                
In this article, we are going to declare the functions that throw errors in TypeScript. A function can throw an error if the logic is not correct or you can deliberately declare the function that always throws an error. A function can be created with the different return types with the required type of value it returns. We will create the error fun
                
How to Declare Variables with Explicit Types in TypeScript ?
                
In TypeScript, you declare variables with explicit types by specifying the type of the variable after its name using a colon (:) followed by the desired data type which can be string, number, etc. Example 1: Here, the variable age is explicitly declared with the type number. This means it can only store numerical values, and TypeScript will enforce
                
How to Declare Parameters with Default Values in TypeScript ?
                
The parameters can be assigned with a default value at the time of declaring a function. You can simply give an initial value to the parameter which you want to make default. So that, if someone does not pass any value for that parameter it considers that initial value and executes the code without any errors. In TypeScript, while declaring the fun
                
How to Declare & use Arrow Functions in TypeScript ?
                
The arrow function is a concise way of declaring the functions in TypeScript with a lexical binding of this object. The arrow function provides us with a shorter way of declaring functions without using the function keyword just with the help of arrows(=>) and the round brackets(). They can be assigned to a variable created using the let, var, a
                
How to Declare Optional Properties in TypeScript ?
                
The optional properties are the properties that may or may not be present in an object or assigned with a value. You can define the optional properties for different data types in TypeScript like interfaces, type aliases, classes, etc. In TypeScript, you can use the question mark (?) symbol to declare the optional properties just after the name of
                
How to Declare Variables in TypeScript ?
                
In TypeScript, a variable can be defined by specifying the data type of the value it is going to store. It will store the values of the specified data type only and throws an error if you try to store the value of any other data type. You can use the colon syntax(:) to declare a typed variable in TypeScript. You need to declare variables in this fo
                
What are the different keywords to declare variables in TypeScript ?
                
Typescript variable declarations are similar to Javascript. Each keyword has a specific scope. Let's learn about variable declarations in this article. In Typescript variables can be declared by using the following keywords: varlet constVar keyword: Declaring a variable using the var keyword. var variable : number = 1;The var variables have functio
                
How to Declare an Array of Strings in TypeScript ?
                
Arrays are fundamental data structures in TypeScript, enabling developers to manage collections of elements efficiently. Below are the approaches to declare an Array of strings in TypeScript: Table of Content Square Brackets NotationArray ConstructorSquare Brackets NotationUsing square brackets notation is the most common and straightforward method
                
How to declare a module in TypeScript ?
                
A module is a piece of code that can be called or used in another code. There is nothing new about modules in Typescript. The concept of the module was introduced by JavaScript with ECMAScript 2015 release. Typescript is just re-using this feature. Will the code not work without Modules? Of course, it will. The code will still work. But there are m
                
How to Declare a Fixed Length Array in TypeScript ?
                
To declare a Fixed-length Array in TypeScript you can use a Tuple. Tuple types allow you to specify the types for each element in the array and, importantly, define a fixed number of elements in a specific order. In this article, we are going to learn how to declare a fixed-length array in TypeScript. Syntax type FixedLengthArray = [Type1, Type2, .
                
Explain when to use "declare" keyword in TypeScript
                
In TypeScript, the “declare” keyword is important in ambient declarations. These declarations allow us to integrate third-party JavaScript libraries seamlessly into our TypeScript codebase. Think of it as a bridge that connects TypeScript with existing JavaScript code. In this article, we’ll explore when and how to use the “declare” keyword effecti
                
How to Declare an Empty Array in TypeScript?
                
TypeScript provides a robust type system that allows you to define and manage data structures more effectively than in plain JavaScript. One common task is declaring empty arrays with specific types, ensuring that your array holds only values of the intended type. These are the following ways to declare an empty array in TypeScript: Table of Conten
                
How to Declare the Return Type of a Generic Arrow Function to be an Array ?
                
In TypeScript, declaring the return type of a generic arrow function to be an array is generally essential when we want to ensure that the function always returns the array of a particular type. This is especially necessary for maintaining type safety and maintaining consistency in our code. Declaring the return type as an array, one can avoid unin
                
How to create a new object from the specified object, where all the keys are in lowercase in JavaScript?
                
In this article, we will learn how to make a new object from the specified object where all the keys are in lowercase using JavaScript. Example: Here, we have converted the upper case to lower case key values. Input: {RollNo : 1, Mark : 78} Output: {rollno : 1, mark : 78} Approach 1: A simple approach is to Extract keys from Object and LowerCase to
                
Difference between Object.keys() and Object.entries() methods in JavaScript
                
Object.keys() and Object.entries() are methods in JavaScript used to iterate over the properties of an object. They differ in how they provide access to object properties: Object.keys() returns an array of a given object's own enumerable property names, while Object.entries() returns an array of a given object's own enumerable string-keyed property
                
Difference Between Object.keys() and Object.getOwnPropertyNames() in JavaScript
                
In JavaScript, Object.keys() and Object.getOwnPropertyNames() both retrieve properties of an object but differ in scope. Object.keys() returns an array of an object's own enumerable property names. In contrast, Object.getOwnPropertyNames() returns an array of all own property names, including non-enumerable properties. These methods are useful for
                
Typescript Awaited<Type> Utility Type
                
In this article, we are going to learn about the Awaited<Type> in TypeScript. It is a programming language that is a strict syntactical superset of JavaScript. It adds optional static typing and class-based object-oriented programming to JavaScript, one of the features of the typescript is Awaited<Type> it is a utility type in TypeScrip
                
TypeScript Extract<Type, Union> Utility Type
                
In this article, we are going to learn about Extract<Type, Union> utility type in TypeScript, TypeScript is a strongly typed programming language that builds on JavaScript, giving you better tools at any scale. Extract<Type, Union> utility type is used to extract a subset of types from a union type that matches a certain criterion, This
                
TypeScript Readonly <Type> Utility Type
                
In this article, we are going to learn about Readonly<Type> Utility Type in Typescript. Typescript is a popular programming language used for building scalable and robust applications. One of the features of Typescript is Readonly<Type> Utility Type which is used to create a new type where all properties are readonly, meaning they canno
                
TypeScript ThisParameterType<Type> Utility Type
                
In this article, we are going to learn about ThisParameterType<Type> Utility Type in Typescript. TypeScript is a popular programming language used for building scalable and robust applications. In TypeScript, the ThisParameterType<Type> utility type is used to extract the type of this parameter in a function type. It allows you to captu
                
TypeScript OmitThisParameter<Type> Utility Type
                
In this article, we are going to learn about OmitThisParameter<Type> Utility Type in Typescript. TypeScript is a popular programming language used for building scalable and robust applications. In TypeScript, the OmitThisParameter<Type> utility type is used to create a new function type that is the same as the input Type but with this p
                
TypeScript NonNullable<Type> Utility Type
                
In this article, we are going to learn about NonNullable<Type> Utility Type in Typescript. TypeScript is a popular programming language used for building scalable and robust applications. In TypeScript, the NonNullable<Type> utility is used to create a new type by removing null and undefined from the given type. It ensures that the resu
          
Company
About Us
Legal
In Media
Contact Us
Advertise with us
GFG Corporate Solution
Placement Training Program
GeeksforGeeks Community
Languages
Python
Java
C++
PHP
GoLang
SQL
R Language
Android Tutorial
Tutorials Archive
DSA
Data Structures
Algorithms
DSA for Beginners
Basic DSA Problems
DSA Roadmap
Top 100 DSA Interview Problems
DSA Roadmap by Sandeep Jain
All Cheat Sheets
Data Science & ML
Data Science With Python
Data Science For Beginner
Machine Learning
ML Maths
Data Visualisation
Pandas
NumPy
NLP
Deep Learning
Web Technologies
HTML
CSS
JavaScript
TypeScript
ReactJS
NextJS
Bootstrap
Web Design
Python Tutorial
Python Programming Examples
Python Projects
Python Tkinter
Web Scraping
OpenCV Tutorial
Python Interview Question
Django
Computer Science
Operating Systems
Computer Network
Database Management System
Software Engineering
Digital Logic Design
Engineering Maths
Software Development
Software Testing
DevOps
Git
Linux
AWS
Docker
Kubernetes
Azure
GCP
DevOps Roadmap
System Design
High Level Design
Low Level Design
UML Diagrams
Interview Guide
Design Patterns
OOAD
System Design Bootcamp
Interview Questions
Inteview Preparation
Competitive Programming
Top DS or Algo for CP
Company-Wise Recruitment Process
Company-Wise Preparation
Aptitude Preparation
Puzzles
School Subjects
Mathematics
Physics
Chemistry
Biology
Social Science
English Grammar
Commerce
World GK
GeeksforGeeks Videos
DSA
Python
Java
C++
Web Development
Data Science
CS Subjects
        
 
        We use cookies to ensure you have the best browsing experience on our website. By using our site, you
        acknowledge that you have read and understood our
        Cookie Policy &
        Privacy Policy
        Got It !