TypeScript versus JavaScript: Which one to use?

While talking with other devs, the topic of whether and/or when to use TypeScript over JavaScript often comes up.

I've heard a number of criticisms:

• It slows down development.
• The build setup is more complex.
• The errors can sometimes be very cryptic.
• It's not worth it for smaller projects.

While those are valid concerns, things are not as cut and dry. While TypeScript can seem daunting, I've found the more you immerse yourself in learning it, the advantages and trade-offs become apparent.

What is TypeScript?

TypeScript is a superset of JavaScript that adds static typing to the language.

In simple terms:

• TypeScript is essentially JavaScript with optional type annotations.
• It compiles (or transpiles) to plain JavaScript so it can run in any browser, Node.js, or JavaScript environment.

Here's a basic example:

JavaScript

function greet(name) {
  return 'Hello ' + name.toUpperCase();
}

TypeScript

function greet(name: string): string {
  return 'Hello ' + name.toUpperCase();
}

In the TS example above, if you were to pass an argument with the type of number (instead of string) to greet(), TypeScript will throw a compile-time error and alert you to the type mismatch.

In JavaScript you wouldn't get an error at compile time, you would get it during runtime when the number you passed doesn't find .toUpperCase() as an available method, or even worse depending on the use case, you might ship the code with a bug your end users will unfortunately discover.

How TypesScript works and who uses it?

How it works:

• Instead of .js, .jsx files. You write .ts or .tsx files.
• The TypeScript compiler (tsc) or tools like Babel turn it into .js files.
• The output runs exactly like normal JavaScript.

Who uses it:

• It is popular with frontend developers (React, Angular, Vue)
• Common in backend development with Node.js
• Used by companies like Microsoft, Google, Slack, Airbnb, and Stripe etc.

What are the advantages of TypeScript over JavaScript?

TypeScript offers some key advantages over JavaScript:

Static Typing

• Catch errors at compile time rather than at runtime.
• Improves editor tooling, such as autocompletion and type hints.
• Helps prevent common bugs, like passing the wrong type of argument to a function.

Improved Developer Experience

• Better IDE support (e.g., VS Code) with features like intelligent code completion, inline documentation, and refactoring tools.
• Makes it easier to understand codebases, especially in teams or large projects.

Code Readability and Self-Documentation

• Types serve as explicit documentation, making code more predictable and understandable.
• Easier onboarding for new developers who can see what types of data are expected.

Scalability

• TypeScript shines in large-scale applications with many developers and components.
• Helps enforce architectural boundaries and clear contracts between different parts of the system.

Refactoring Confidence

• Types give you confidence to refactor code safely.
• Catch broken references or incorrect assumptions during the build process.

Modern JavaScript Features + Compatibility

• TypeScript supports the latest ECMAScript features, even before they are widely supported by browsers.
• You can compile down to ES5/ES6 to maintain compatibility.

Better Integration with Modern Frameworks

• Frameworks like React, Angular, and Vue have first-class TypeScript support.
• Many libraries provide TypeScript definitions (via DefinitelyTyped or native support).

When should you consider using TypeScript over JavaScript?

Building a Large or Long-Term Project

• TypeScript provides structure and safety that's essential for scaling.
• Easier to maintain and refactor as the codebase grows.
• Helps enforce consistent contracts across modules and teams.

Working on a Team

• Shared code benefits from TypeScript's self-documenting types.
• Makes it easier for new team members to onboard and understand code.
• Reduces bugs due to miscommunication about function inputs/outputs.

Using Modern Front-End Frameworks

• Frameworks like React, Angular, and Vue 3 have excellent TypeScript support.
• You’ll get better tooling, autocompletion, and type safety for props, states, context, etc.

Needing Refactor-Friendly Code

• If you plan to refactor regularly, TypeScript will help catch issues early.
• Greatly reduces the fear of breaking things when changing code.

Writing APIs, Libraries, or SDKs

• If others will use your code (like a library or shared service), TypeScript gives them intelligent tooling and type-safe interfaces.

Using Complex Data Structures or Domain Logic

• When your code deals with nested objects, APIs, or business logic, TypeScript's types help model data clearly and avoid mistakes.

So when might you just stick with JavaScript?

There are valid scenarios where JavaScript makes more sense.

• When the script is small or the tool is a one-off.
• Rapid prototyping or MVPs where setup speed matters more than long-term maintainability.
• Environments where build steps are undesirable or not feasible.

But what about the criticisms?

It slows down development.

The slow down in development is short term, TS requires more boilerplate up front (e.g., defining interfaces, types). If you are in a situation where you are rapid prototyping, especially for small features or quick fixes, you may find TS more trouble than it's worth. However if you are building a long lasting application, and especially as the complexity increases, TypeScript will be worth the short slow down.

The build setup is more complex.

TypeScript requires transpilation to JavaScript, adding a build step, and it may introduce tooling overhead when configuring Babel, Webpack, tsconfig, etc. That may be true, but that being said, many modern build tools such as Vite or Parcel, make this a lot easier than it used to be.

The errors can sometimes be very cryptic.

Some error messages (especially with advanced types or generics) are hard to decipher. Debugging type errors can take as long or longer than fixing runtime bugs. While many TypeScript errors are pretty straight forward there are ones that can take longer to decipher, but I've found as you continue to use TypeScript, these errors are fewer and farther between.

It's not worth it for smaller projects.

For scripts or small front-end apps, the overhead of setting up TypeScript may outweigh its benefits. But if you are in a situation where you are dealing with a project that will need to scale and increase in complexity as development continues, TypeScript is a great way to ensure more predictable and easier to refactor code.

So what's the verdict?

If you plan to refactor regularly, TypeScript will help catch issues early and greatly reduces the fear of breaking things when changing code. In my opinion it's like having an extra layer of testing built in that can alert and assist a developer in identifying, debugging, and fixing bugs before they ever make their way out of the developers local environment.

TypeScript helps you write safer, more maintainable, and more scalable code. While there’s a slight learning curve and initial setup overhead, the long-term productivity gains, especially in medium to large projects far outweigh the downsides.