Top Mistakes of Beginner TypeScript Developers: How to Avoid Them

Top mistakes of beginner TypeScript developers: how to write clean and safe code

TypeScript is a powerful tool that helps developers write more predictable and safe JavaScript code. However, when switching from JS, many beginners make the same mistakes, negating the benefits of strict typing. In this article, we will analyze the 4 most common mistakes of beginner TypeScript developers and show how to fix them using clear examples.

1. Overusing the any type

The most common and dangerous mistake is using any everywhere TypeScript asks you to specify a type. This turns your code back into regular JavaScript, depriving you of editor hints and type checking during compilation.

❌ Bad example:

function processData(data: any) {    return data.name.toUpperCase();}

const result = processData(42); // Runtime error! Number has no property name

✅ Good example:

interface UserData {    name: string;    age: number;}

function processData(data: UserData): string {    return data.name.toUpperCase();}

const user: UserData = { name: "Ivan", age: 30 };const result = processData(user); // Works correctly

Tip: Try to use unknown instead of any if the type is truly unknown. unknown will force you to perform a type check before using the value.

2. Ignoring Strict Mode

Many beginner developers disable strict mode (strict: true) in tsconfig.json to "not get distracted by errors". This deprives you of the main advantage of TypeScript — early detection of potential bugs.

What Strict Mode includes:

• strictNullChecks — prohibits assigning null and undefined to variables unless explicitly stated.
• noImplicitAny — prohibits the implicit use of any.
• strictFunctionTypes — stricter checking of function types.

❌ Without Strict Mode:

function getLength(value: string | null) {    return value.length; // Runtime error if value = null}

✅ With Strict Mode:

function getLength(value: string | null): number {    if (value === null) {        return 0; // Handle null explicitly    }    return value.length; // TypeScript knows value is a string}

Tip: Always enable "strict": true in tsconfig.json. This will save hours of debugging in the future.

3. Incorrect work with asynchrony

Errors with promises and async/await are classics. Beginners often forget to handle errors or incorrectly type asynchronous functions.

❌ Bad example:

async function fetchData(url: string) {    const response = await fetch(url);    const data = response.json(); // Forgot await!    return data;}

✅ Good example:

interface ApiResponse {    id: number;    title: string;}

async function fetchData(url: string): Promise<ApiResponse> {    try {        const response = await fetch(url);        if (!response.ok) {            throw new Error(`HTTP error! status: ${response.status}`);        }        const data: ApiResponse = await response.json();        return data;    } catch (error) {        console.error("Error loading data:", error);        throw error; // Rethrow the error    }}

Tip: Always use try...catch to handle errors in asynchronous functions and don't forget await when calling methods that return a promise.

4. Ignoring