5 Reasons To Use TypeScript

This post was originally posted on my blog, 5 Reasons To Use TypeScript. Some changes have been made from the original post to fit the styling of dev.to. I recommend reading the post on the original site to see it styled as intended.

The rise of TypeScript seems to have happened slowly, then all at once (like ketchup coming out of the bottle).

Over the past five years, it has continued to grow in popularity until it is now by far the most liked "JavaScript flavour". According to the State of JS 2020 survey, TypeScript is now one of the most used frontend technologies and one with the highest positive opinions.

As I mentioned in my previous post, I was sceptical, but have grown to love TypeScript so that I would recommend it as the default flavour for any new JavaScript project. TypeScript had so many benefits that I hadn't appreciated before I tried it.

In this post, we'll take a look at five of those benefits:

• Compile-Time Errors
• Clearer Code
• Tooling Over Documentation
• Safe Refactoring
• Incredible Autocomplete

1. Compile-Time Errors

Let's get this out of the way first - the obvious benefit to using TypeScript is compile-time errors for type safety.

Did you forget to check if a value is null? Typescript won't.

Missed a case in a switch statement? Typescript won't.

Added an argument to a function but overlooked the existing uses of the function? Typescript won't.

This is generally how people describe TypeScript. It means that, from my experience, when people are hesitant about whether TypeScript is worth the extra effort, this is all they're thinking about.

Compile-time errors are useful, but it's the secondary benefits that you get because of the type checking that makes TypeScript really exciting.

2. Clearer Code

TypeScript requires you to be more explicit with your code and with your mental model of how the code works.

It is said that writing forces you to clarify your thinking. It's so hard to write what's in your head - attempting to write it down forces you to organise your thoughts, challenge your assumptions, question whether there is a better way. TypeScript is the equivalent of frontend development.

Programming is hard. There are huge amounts of complexity. TypeScript restricts the freedom of JavaScript, but by doing so, it reduces the complexity of the code. This makes it a lot easier to catch bugs and move forward with confidence with what we're writing.

TypeScript reduces the complexity of the code. That may surprise you. One of the common complaints against TypeScript is how complicated it is. Sure, the basic use cases may be easy, but pretty soon you're down a rabbit hole with type-generics and conditional types and you're spending more time reading the TypeScript documentation than actually coding.

When this happens to me, 9 times out of 10 that's a flag that my code is too complicated. When I think about what I'm trying to do, I can usually simplify my data structures and function signatures. The advanced parts of TypeScript are positive friction, slowing me down enough to question whether there are better ways of designing my app.

"If you find yourself struggling with writing types or you're basically spending time developing your types instead of developing your app, maybe the code you're writing is too complicated." - Ben Ilegbodu

3. Tooling Over Documentation

Documentation is essential for the long-term health of a project. However, it's also easy to neglect, hard to enforce, and can't report if it is no longer up-to-date. So if it's possible, tooling should be prioritised over documentation.

When I started working at a new company, part of my onboarding involved reading the company's coding style guide. I skimmed through it, but very little stayed in my head. I told myself once I was coding, I would refer back to the style guide to make sure I was following the standards. Unsurprisingly, I never did.

Tools like ESLint and Prettier document your code styles. But they go a step further and enforce those styles while you're coding. You no longer need to worry about stray console.logs or inconsistent semi-colons. Instead of the style guide being one extra thing you have to hold in your head, it becomes something you don't even have to think about. You just focus on what really matters.

TypeScript is a tool that forces you to extract knowledge out of the developer's head and into the code. It documents what arguments a function is expecting, what shape objects are, and which variables may be undefined. And it will remind you when it is no longer up to date and where exactly you need to update.

Without TypeScript, so much redundant time is spent by each developer having to track down the shapes of objects. It requires searching through documentation and praying they are up-to-date. Or it requires debugging the code and praying your guesses of which fields are required/optional are correct.

TypeScript is an up-front investment that saves you and your team much more time in the future.

"TypeScript shines on a team. Even if the team is you and you-from-6-months-ago" - @swizec

4. Safe Refactoring

I recently had two refactoring experiences that were a world apart.

In the first case, I was updating all our buttons to use our common Button component. It was a straightforward change, and completely terrifying. The codebase was JavaScript, there were too many buttons to manually check each one and our test coverage was spotty at best. It felt like I was walking on the edge of a cliff, knowing that if I missed or misspelt a prop, that could potentially stop a button from working - a critical bug.

In another refactor, I was changing the shape of the state. Originally we just needed a list of titles but now we needed a title and a description for each item. Fortunately, this time I was working on a TypeScript codebase so I updated the type from string[] to { description: string; title: string; }[] and then just let TypeScript tell me exactly what would need updating. It was only halfway through that I suddenly realised how hard this could potentially be in JavaScript. Instead, I hardly needed to think at all.

TypeScript not only gives you confidence that you haven't missed anything when you refactor but also shows you where you need to update. You no longer need to manually track your variables all over the code - just follow the red squiggles.

5. Incredible Autocomplete

This section assumes you're using VSCode as your IDE. Both TypeScript and VSCode are developed and maintained by Microsoft so are designed to integrate well with each other.

Other IDEs have TypeScript plugins which also give you Autocomplete. However, I have no experience with using them, so can't comment on how good they are.

The TypeScript autocomplete unexpectedly has become one of the biggest reasons why I love TypeScript. I imagine it's one of the reasons why it's so popular among developers.

Autocomplete means I don't have to worry about typos (did we name this prop color or colour?). I don't have to keep jumping between files to see which component props I need. I don't need to keep googling the names of string and array functions.

Let's say I have a string variable that could be undefined - string | undefined. I want to see if the string, contains a '#' character but I can't remember if I should be using .contains or .includes (happens every time!). I enter the variable name, press . and all the possible string functions are shown to me:

I find the function I want and press tab to select it:

Did you see that? Not only did it help us look up which function we wanted, but it also filled it in for us and used optional chaining to make sure we handle the cases where it's undefined. 🤯

All these mean you don't have to keep interrupting your flow. You can just tab and move on to the next thing. It's like having a co-pilot as you code.

TypeScript As A Default For New Projects

TypeScript isn't perfect. There are plenty of arguments against it (some better than others). But for me, TypeScript should be the default for any new project. Instead of asking if there is a good reason to include it, you should be asking if there is a good reason not to.

Comments

[RRKallan]

nice to have Compile-Time Errors.
But Most of the time data used in JS is dynamic. So cool to have compile error, but what if data has different type as expected. It will throw a error and application isn't useable anymore.

Clear code when using Typescript? I disagree. There readability of code most of the times is very hard

Safe Refactoring
you are changing a type! These type check could also be done with propTypes or Flow. 2 tools which are var way faster then typescript on development time. And Safer there they do the check on run time. So check the console output of your browser

Incredible Autocomplete
Hope this is a joke, there i have full compatibility of auto-completion of JS code

TypeScript As A Default For New Projects
My opinion is a big NO. It woud help on code time. But the ability of bug fixing on runtime is not in scope, and these developers would always point to external excuses. And aren't able to find the problem of the bug without doing a lot of debuggers.
Also Javascript isn't a type programming. Typescript will be translate to Js with out typechecking.
Also to compile in development takes more time.

[Babak K. Shandiz]

Data validation is a totally different thing than strong typing. The latter ensures your codebase is consistent regarding various data types flowing through it, whereas data validation asserts runtime input compatiblility (of course from outside world, AKA application boundaries) with what the code expects.

While strong-typing is not a must (however makes design/develop a whole lot easier and insightful,) but validation is always required, no matter what programming language or platform you use.

If that helps, as a metaphor, data validation is like the security guard that verifies legitimacy of people entering a military base and makes sure everyone is suited with their formal camo with visible names/ranks, while strong-typing is like the set of military rules that defines the hierarchy and the chain of command.

[RRKallan]

@jfbrennan & @babakks
nice clarifications.

As developer i learned and will teach also defend programming.

@lukeshiru
I strongly advice you to be open for different views. Listen and try to understand the arguments. Try to avoid putting people in a box, saying they didn't actually did any real work, they missing points etc etc. Changing given examples to proof your vision.

[RRKallan]

const typedAdd = (value1: number) => (value2: number) => value1 + value2;

Will be after transpiling and production ready

const x = (a) => (b) => a + b

So after building a production build all your ts type check will be gone.
And therefore your function will except all kind of types.

You mean the same propTypes that were removed from the core of React because we have TypeScript and the same Flow that nobody wants to use nowadays?

propTypes is removed from the core because the vision of react is that you must be able to configure your dev app as you want and with the most minimum amount of package size.

It depends. Yes, you get autocompletion of JS but only when the editor can infer the types of stuff or you added the proper JSDocs for that.

I had never problems with auto completion with my created libs in JS. And still I doesn’t have
Yes when your lib has a .ds.ts file it will only use the declared and exported for auto completion

And JS is a typed system, just because you don't write the types it doesn't mean you don't have them.

JS isn’t a type program. TS is a superset of JS. To be able to run your code it needs to be transpiled to JS. JS doesn’t care if value changes from type.

Even with unit or e2e test you can’t prevent when api gives you a different type then discribe with TS. Also on production there is no type check. Even on development there is no type check on runtime. In that case you don’t see warning / error on development when running your code and calling an api.

I have enough examples in professional business settings where developers couldn’t find the bug. Because they said testing is succes and no compile errors.
And they said there is no bug. But on production the code was failing and throwing an error

[RRKallan]

it usually happens when you didn't actually did any real work with TS

It might be wise not to make assumptions. Assuming I haven't actually worked with TS?
Led multiple projects as lead where we use TS

// Let's say I want `x` to only have numbers, then the code stays the same:
let x = 1; // type is number
x = x + "hello world"; // type of `x` is still number, so error here because you're trying to assign a string to it.

// But now I want `y` to be either a number o a string:
let y: number | string = 1;
x = x + "hello world"; // No errors here, in the line above I said this is actually what I want.

the last x will throw an error with TS

My assumption, it needs to be

let y: number | string = 1;
y = y + "hello world"; 

[RRKallan]

When you use it you have the types, but the browser or node don't need those types, the types are there to help you as a dev

You mis the point that you still need to code checks to prevent unexpected behaviours and crashing application.

const toHex = (value) => value; i get autocompletion in my editor

You really need to read a little more about JS types. JS uses types internally. Just use typeof with a value.

typeof has a disadvantage see example code

console.log(typeof []); // object
console.log(typeof null); // object

to get the correct type of your value

console.log(Object.prototype.toString.call([]).slice(1, -1).split(" ")[1]. toLowerCase()); // array
console.log(Object.prototype.toString.call(null).slice(1, -1).split(" ")[1]. toLowerCase()); // null

I'm expressing myself wrong, to say JS is not a type program. What i meant JS is a weakly dynamically-typed language and type checks are at runtime and it allows implicit conversion between unrelated types

TypeScript / Python is a strongly typed programming language and type checks are on compile-time and doesn’t allow implicit conversions between unrelated types

example JS

let x = 1 // type is number
x = x + "hello world" // type is string
console.log(x);

example Python

x = 1;   #type assigned as number.
x = x + "hello world";   #type-error, string and number cannot be concatenated.
print(x);

[Rammina]

Thank you for sharing your insights about Typescript!
While I do agree with the majority of your points, here are some downsides that make me not use it sometimes.

[RRKallan]

You see, you didn't read what I wrote at all

And again making a wrong assumption. I read your comments.

If the API gives you different values, the problem is not with the types, is elsewhere (API architecture, mainly).

my comment

TypeScript / Python is a strongly typed programming language and type checks are on compile-time and doesn’t allow implicit conversions between unrelated types

your reaction

You're wrong again, but I understand, it usually happens when you didn't actually did any real work with TS.

one of the first things on typescriptlang.org

TypeScript is a strongly typed programming language that builds on JavaScript

and so we can go on.
I notice already you are avoiding given points.
I wish you luck on a national / international big brand, own JS package national / international used.

[RRKallan]

No need to tell me the difference, ether i don't need to google to get now about the differences. And this is exactly a point which i mentioned on my previous comment and is not the first time you do this, not only on me.

As previous said, where my feeling is you are ignoring it, i'm working with TS on my projects, Im up to date and now how to use. On these projects i'm the lead.

The fact is you don't care about runtime behaviour.
In your opinion you have a perfect code with type check on compile / development time.

All unexpected behaviour on runtime is a problem from outside.
Even when your application crash you will point out to external facts, and not your problem.
And i can bet you won't be able to find the bug, or you will need a couple of days to figure out the problem.

[RRKallan]

Good to hear that you don't put people in a "box", and you open for different views :)

From my side, and my assumption of your opinion is as follow.

As i understand your opinion is when using type check, on compile time / development time, is safe enough for your code. And when there is unexpected data coming from example an api, the api needs to deliver as expected.
Based on this it could crash the application because unexpected data. User can't continue and refresh will lead losing data stored with for example Redux.
So my vision is as JS develop you need always be aware and prevent application crash and unexpected behaviours on runtime.