Master TypeScript with these practical examples of the foreach loop.

Table of content

  1. Introduction
  2. What is TypeScript?
  3. Benefits of using TypeScript
  4. Foreach loop basics
  5. Practical example 1: Using foreach to loop over an array
  6. Practical example 2: Using foreach to manipulate DOM elements
  7. Practical example 3: Using foreach with object literals
  8. Conclusion


TypeScript is an open-source language that has gained popularity among developers in recent years. It is a superset of JavaScript and provides additional features such as static typing, classes, and interfaces. One of the most useful features of TypeScript is the foreach loop. It is a syntax that enables you to loop through items in an array, object, or tuple. It is especially useful when dealing with large datasets or when you need to perform a repetitive task on a collection of data.

In this article, we will explore practical examples of using the foreach loop in TypeScript. We will cover how to implement the loop to iterate through different types of data structures and perform operations on them. We will also discuss the benefits of using the foreach loop over other iterations such as for loops or while loops. By the end of this article, you will have a better understanding of how to use the foreach loop in TypeScript and how it can help you write cleaner and more concise code.

What is TypeScript?

TypeScript is an open-source programming language that is an extension of JavaScript. Created by Microsoft, TypeScript was designed to make it easier to build large-scale applications by adding static typing to JavaScript. This means that TypeScript provides developers with additional tools and features that help to catch errors and bugs earlier in the development process.

How does TypeScript work?

TypeScript works by compiling TypeScript code into standard JavaScript code. This means that TypeScript can be used with all modern web browsers and JavaScript frameworks without any additional setup. TypeScript also includes a number of features that are not available in standard JavaScript, such as classes, interfaces, and enums.

What are the benefits of using TypeScript?

There are several benefits to using TypeScript in your web development projects, including:

  • Type checking: TypeScript variables can be defined with specific data types, which helps catch errors and bugs earlier in the development process.
  • Better IDE support: IDEs like Visual Studio Code have excellent support for TypeScript, including code completion, refactoring, and debugging.
  • Increased code readability: TypeScript provides a more structured approach to writing code, which can make it easier to read and maintain over time.
  • Easy adoption: Since TypeScript is an extension of JavaScript, learning TypeScript is relatively easy for web developers who are already familiar with JavaScript.

Overall, TypeScript is a powerful tool for web developers who want to build large-scale applications with fewer bugs and errors.

Benefits of using TypeScript

TypeScript is a powerful and increasingly popular programming language that has gained a lot of attention in recent years. Some include:

  • Type safety: TypeScript offers static type checking, which helps catch errors in your code before they become runtime errors. This makes it easier to maintain larger codebases, and can save you time and effort in the long run.

  • Better code organization: TypeScript offers a number of features that can help you organize and structure your code, such as classes, interfaces, and namespaces.

  • Improved tooling: Because TypeScript is a typed language, it is easier for IDEs and other development tools to provide autocomplete suggestions and other features that can make coding faster and more efficient.

  • TypeScript is versatile: TypeScript can work with a variety of different programming paradigms, including object-oriented and functional programming styles. This makes it a great choice for a wide range of projects and use cases.

  • Powerful language extensions: TypeScript offers a range of language extensions that can make your code more concise and expressive. These include features such as optional chaining, nullish coalescing, and decorators.

Overall, TypeScript offers a number of benefits that make it a great choice for modern web development. Whether you are building a small personal project or a large enterprise application, TypeScript can help you write better code, catch errors earlier, and maintain your codebase more easily over time.

Foreach loop basics

The foreach loop is a common and useful programming construct that allows you to iterate over a collection of items. In TypeScript, the foreach loop is used extensively with arrays and objects.

Here are some basics of the foreach loop in TypeScript:

  • The foreach loop is also called the for…of loop and is used to iterate over arrays, objects, and other iterable objects.

  • The foreach loop syntax is simple and easy to understand:

for(let item of items) {
  // code to execute for each item
  • In this syntax, items is the collection of items that we want to iterate over, and item is a variable used to reference each item in the collection.

  • The foreach loop executes the code for each item in the collection. The loop terminates when all items have been processed.

  • TypeScript provides several built-in functions that make it easy to manipulate arrays using the foreach loop, such as forEach, map, filter, and reduce.

  • When using the foreach loop with objects, we can loop through all the properties of an object by using the Object.keys() method.

  • It is important to note that the foreach loop may not be the best choice for some operations, such as searching or sorting, where the regular for loop may be more appropriate.

Overall, the foreach loop is an essential construct for working with collections in TypeScript. With its simple syntax and powerful capabilities, it is a tool that any TypeScript developer should have in their toolkit.

Practical example 1: Using foreach to loop over an array

One common use case for the foreach loop in TypeScript is to iterate over an array of data. This can be useful in a variety of scenarios, such as processing a list of user submissions or calculating the sum of all values in an array. Let's take a look at an example:

const numbers = [1, 2, 3, 4, 5];
let sum = 0;

numbers.forEach((num) => {
  sum += num;


In this example, we have an array of numbers and a variable called "sum" initialized to 0. We then use the foreach method to iterate over each number in the array and add it to the sum variable. Finally, we log the sum to the console, which should output 15.

Note that we pass an arrow function to the foreach method as a parameter. This function takes one argument (the current element in the array) and updates the sum variable accordingly. You could also declare the function separately and pass it as an argument, like so:

function addNumberToSum(num: number) {
  sum += num;


This achieves the same result as the previous example, but separates the logic of the function from the foreach loop itself.

Overall, the foreach loop is a powerful tool in TypeScript for iterating over arrays and performing operations on their elements. It can greatly simplify your code and make it more readable, especially for complex calculations or data processing tasks.

Practical example 2: Using foreach to manipulate DOM elements

One practical example of using the foreach loop in TypeScript is to manipulate DOM elements on a webpage. When working with web development, it's common to need to select and change the properties of multiple elements at once. The foreach loop can help simplify this process by allowing you to iterate over an array of elements and apply the same changes to each one.

Here's an example of how you could use the foreach loop to change the background color of all paragraph tags on a webpage:

const paragraphs = document.querySelectorAll('p');

paragraphs.forEach((paragraph) => { = 'red';

In this example, we first use the querySelectorAll method to select all paragraph tags on the page and store them in an array. We then use the forEach method to iterate over each paragraph, setting the backgroundColor style property to red for each one.

This is just one example of how the foreach loop can be used in TypeScript for practical web development tasks. The ability to quickly and easily apply changes to multiple elements at once can be a huge time-saver when building complex web applications.

Practical example 3: Using foreach with object literals

In this practical example, we'll explore how to use the foreach loop with object literals in TypeScript. Object literals are a convenient way to define small, self-contained objects in TypeScript, and are commonly used for tasks such as data validation and configuration.

Let's say we have an object literal representing a user's information, with properties for their name, age, and email address. We can use the foreach loop to iterate over each key-value pair in the object, and print out the value of each property.

const user = {
  name: 'John Doe',
  age: 30,
  email: ''

for(const [key, value] of Object.entries(user)) {
  console.log(`${key}: ${value}`);

In this example, we're using the Object.entries() method to convert the user object into an array of key-value pairs. This allows us to use destructuring to assign the key and value to variables in the foreach loop. We then use string interpolation to print out each key-value pair in a readable format.

Using foreach with object literals is a powerful way to manipulate data in TypeScript, and is commonly used in web development and data science applications. By mastering the foreach loop, you'll be able to easily iterate over complex data structures and perform a wide range of operations with minimal boilerplate code.


In , the forEach loop is a useful feature in TypeScript that allows you to iterate over arrays and perform actions on each item in the array. Whether you're working on a web application, a mobile application, or a desktop application, the forEach loop is a versatile tool that can help you perform complex tasks with ease.

In this article, we've covered various practical examples of using the forEach loop in TypeScript. We've seen how to use it to iterate over an array of strings, an array of objects, and even an array of arrays. We've also learned how to use it with different TypeScript features such as interfaces, arrow functions, and even asynchronous code.

By mastering the forEach loop, you'll have a powerful tool in your arsenal that can help you write more efficient and effective code. With the examples we've covered in this article, you have a solid foundation to start exploring more advanced use cases for the forEach loop in TypeScript.

So, whether you're a seasoned developer or just starting out with TypeScript, be sure to spend some time mastering the forEach loop. It's a skill that will pay off in many different contexts, and it's sure to make your code more robust and efficient.

Throughout my career, I have held positions ranging from Associate Software Engineer to Principal Engineer and have excelled in high-pressure environments. My passion and enthusiasm for my work drive me to get things done efficiently and effectively. I have a balanced mindset towards software development and testing, with a focus on design and underlying technologies. My experience in software development spans all aspects, including requirements gathering, design, coding, testing, and infrastructure. I specialize in developing distributed systems, web services, high-volume web applications, and ensuring scalability and availability using Amazon Web Services (EC2, ELBs, autoscaling, SimpleDB, SNS, SQS). Currently, I am focused on honing my skills in algorithms, data structures, and fast prototyping to develop and implement proof of concepts. Additionally, I possess good knowledge of analytics and have experience in implementing SiteCatalyst. As an open-source contributor, I am dedicated to contributing to the community and staying up-to-date with the latest technologies and industry trends.
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