TypeScript vs. JavaScript: Side-by-Side Comparison

TypeScript and JavaScript, both, are used for building dynamic and interactive web applications. Initially, JavaScript was designed for client-side scripting in web browsers and later used in server-side also. TypeScript is a modern language and is a superset of JavaScript with additional features such as compile-time type safety.

It is worth noticing that TypeScript code is eventually compiled (by transpiler) into standard JavaScript code that can be executed in any browser.

1. A Quick Comparison between TypeScript and JavaScript

The most glaring difference between JavaScript and TypeScript is that JavaScript lacks the type system. What it means is that variables in JavaScript can store any arbitrary value without raising any warning/flag. It often causes unexpected and hard-to-debug errors at runtime. TypeScript’s type system prevents such value assignments and thus helps in reducing such errors.

Additionally, TypeScript’s type system makes the source code more readable and maintainable, similar to any other programming languages

Let us start with a concise comparison of TypeScript and JavaScript in tabular form.

Now, let us delve into specific aspects and explore how both languages differ from each other.

2. Typing

JavaScript is dynamically typed, meaning we don’t need to declare the data type of a variable explicitly. Types are determined at runtime based on the values assigned to variables.

var temp = 42;
typeof temp;   // 'number'

temp = "Hello, world!";      // No type error at compile time
typeof temp;   // 'string'

In TypeScript, we must explicitly declare the types of variables, parameters, and return values. If a variable is declared as a given type, it is not allowed to arbitrarily change its type later on in the program. This helps in catching the type errors in compile time.

In the following example, we cannot assign the string ‘Hello, world!‘ to the variable temp, because initially it has been declared as type ‘number‘.

let temp: number = 42;
temp = "Hello, world!";      // Type error at compile time: Type '"Hello, world!"' is not assignable to type 'number'

3. Compilation

JavaScript code is executed directly by browsers or JavaScript engines. No compilation step is required.

console.log("Hello, JavaScript!");

TypeScript code needs to be compiled into JavaScript before execution. The TypeScript transpiler verifies the variable types and finally generates JavaScript code.

const message: string = "Hello, TypeScript!";
console.log(message); // Needs to be compiled to JavaScript before execution

4. Tooling Support

The one big advantage of TypeScript’s type system is that IDEs can include compilation, validation and refactoring capabilities to any language. This is never possible with a language without the type-safety checks.

For this reason, modern IDEs provide a lot of advanced features for TypeScript projects, whereas for JavaScript projects, only basic tooling support is provided.

5. Error Detection

In JavaScript, errors related to type mismatches or undefined variables might only surface at runtime, making debugging potentially more challenging.

const x = 5;
const y = "10";

const sum = x + y; // Concatenation instead of addition
console.log(sum); // Unexpected Output: "510"

The TypeScript compiler checks types at compile time, catching type-related errors before code execution. This leads to more reliable code.

const x: number = 5;
const y: string = "10";

// Type error at compile time: Operator '+' cannot be applied to types 'number' and 'string'
const sum: number = x + y; 

6. Browser Support

JavaScript is supported by all major web browsers, making it suitable for front-end scripting. In the following example, we create a user object and pass it to the greetUser() method.

// Create a user object
const user = {
    id: 1,
    name: "John Doe"
};

// Define a function that greets the user
function greetUser(user) {
    return `Hello, ${user.name}!`;
}

TypeScript code is compiled into JavaScript, which is then executed by browsers. TypeScript itself isn’t natively supported by browsers. The following code uses the interface type which is not supported by the typescript.

interface User {
    id: number;
    name: string;
}

function greetUser(user: User): string {
    return `Hello, ${user.name}!`;
} 

7. Compatibility

JavaScript is backward compatible with TypeScript. We can use existing JavaScript code within TypeScript projects.

TypeScript can be gradually introduced into existing JavaScript projects, as TypeScript files can coexist with JavaScript files.

8. Use Cases

JavaScript is commonly used for general web development, creating interactive frontend elements, and server-side applications using Node.js.

TypeScript is favored for larger projects where code maintainability, scalability, and type safety are crucial. It’s popular for frontend development and backend applications with Node.js.

9. Performance

JavaScript is interpreted and its execution happens directly in the browser. So it is obviously faster to write the code and run it on the browsers. However, lack of type-safety can cause buggy code and thus eventually hamper the performance.

TypeScript, on the other hand, introduces static typing and advanced features through transpilation to plain JavaScript. It helps catch errors during development, resulting in more predictable code at runtime. It leads to better performance as type errors are caught before execution.

Additionally, TypeScript’s transpilation can produce even more optimized code than a normal developer, potentially leading to more efficient execution.

10. Conclusion

In conclusion, we can say that both languages are suitable for web development, and they do not replace each other. To pul in simple words, TypeScript is a type-safe and technically more correct way to write JavaScript in large projects with high maintenance requirements.

Happy Learning !!