JavaScript vs TypeScript: A Comprehensive Comparison

Introduction

TypeScript extends JavaScript by adding optional static typing and other powerful features. This guide explores the core differences between plain JavaScript vs TypeScript and helps assess when to use each.

What is TypeScript?

TypeScript is an open source language that builds on JavaScript by adding static type checking and type annotations. It provides:

• Static typing to catch bugs early
• Advanced features like interfaces, generics and enums
• Non-JavaScript features like tuples and union types
• Access to emerging JS features before widespread support

TypeScript compiles down to plain JavaScript so runs anywhere JavaScript runs. But it adds robustness during development.

TypeScript Static Typing

A core difference is TypeScript’s support for static typing:

function add(x: number, y: number): number {
  return x + y;
}

add('5', 7) // Errors

This function signature defines x and y as numbers. Calling with a string fails compile-time checking.

Types provide safety nets by preventing invalid operations. They also enable rich IDE tooling for autocomplete, documentation and refactoring.

Type inference even allows omitting types in many places:

const x = 5; // x inferred as number

TypeScript inserts no runtime overhead – types are erased during compilation.

Built-in Types

TypeScript includes a wide selection of built-in types:

• Primitive – string, number, boolean, null, undefined, symbol
• Object – Any, Void, Object
• Collection – Array, Tuple
• Class – Custom classes and constructor signatures
• Function – Parameters, call signatures and return types

Advanced types like enums, generics and union types provide additional flexibility:

type MyBool = True | False; // Custom enum 

function parse<T>(data: string): T {
  // ...
} // Generic function

let x: number | string = 'test'; // Union type

Overall, TypeScript provides a rich type system that catches bugs and provides clarity.

TypeScript Features

Beyond typing, TypeScript adds many other features:

• Interfaces – Define contracts for objects and classes
• Generics – Reusable logics for multiple types
• Enums – Named constants
• Tuples – Fixed-length array alternatives
• Symbols – Unique constant identifiers
• Namespaces – Internal modules for grouping
• Mixins – Composable class extensions
• Decorators – Annotate and modify classes and members

These enhance code organization, reuse and flexibility.

Configurable Checking

TypeScript balances safety and productivity through configurable static analysis.

Enable as little or much strictness as you want:

// tsconfig.json
{
  "compilerOptions": {

    // Strictness flags
    "strict": true,
    "noImplicitAny": true,
    "strictNullChecks": true
  }
}

Start minimally and dial it up over time. This avoids overwhelming legacy codebases with thousands of new errors.

JavaScript Interoperability

Since TypeScript compiles to JavaScript, it integrates seamlessly:

// MyLib.js
export function greet(name) {
  return 'Hello ' + name;
}

// App.ts
import { greet } from './MyLib';

greet('John');

Use npm JavaScript with TypeScript and incrementally migrate JavaScript to TypeScript over time.

JavaScript vs TypeScript

When to Use Each

Given the synergies, when should you choose plain JavaScript vs TypeScript?

Use JavaScript for:

• Smaller, simple codebases
• Code requiring max runtime performance
• Dynamic code leveraging runtime reflection
• Code that will remain largely static

Use TypeScript for:

• Larger, complex codebases
• Code collaboratively written on teams
• Code that will continuously evolve
• Runtime type integrity is important
• Leveraging rich editor tooling

Converting from JavaScript to TypeScript

To incrementally adopt TypeScript, rename JS files to .ts and leverage features:

• Add types to function signatures
• Use interfaces for contracts
• Annotate class properties
• Enable stricter checks gradually

Converting fully does require eventually adding types everywhere. But adopt at your own pace.

Conclusion

TypeScript enhances JavaScript with optional typing and other features like enums, generics, and interfaces. It compiles down to standard JavaScript.

Use TypeScript for large, complex web applications that demand:

• Early bug catching
• Enhanced tooling
• Long term maintainability
• Scalable code organization

For smaller projects or latency sensitive code, plain JavaScript may be preferable.

Know when to leverage each language based on your requirements and priorities for robustness, velocity and runtime performance.

Frequently Asked Questions

Q: Does TypeScript add runtime overhead?

A: No – TypeScript’s static types are completely erased after compilation so they incur no runtime cost.

Q: Can JavaScript and TypeScript work together?

A: Yes, seamlessly. TypeScript integrates beautifully with all JavaScript libraries and runtimes.

Q: Is TypeScript only beneficial for large teams?

A: No – Even solo developers can gain significant velocity boosts from TypeScript’s tooling and avoidance of silly bugs.

Q: Does TypeScript require relearning JavaScript?

A: Not at all. TypeScript is just a superset – any JavaScript code is already valid TypeScript. You can adopt features incrementally.

Q: What JavaScript features does TypeScript not support?

A: Very few – decorators, private fields, and runtime reflection rely more on JavaScript’s dynamism. But workarounds exist.