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Get Started With TypeScript in 2019

Robert Cooper on January 20, 2019

Get Started With TypeScript in 2019 Originally posted on my blog Based on the Stack Overflow Developer survey in 2018, TypeScript is ...

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Tomek Buszewski • Jan 24 '19

Hey Robert, great article!

I am using TypeScript myself and, to be frank, at first I thought bad about it. But then I went to a project without any typing and I saw the benefits from static typings :)

One question though. When I work with large objects, for example a response from REST, and doing a model, should I write the entire interface for it? It can have many optional fields, given the quality of the API itself. How should I approach it?

Robert Cooper • Jan 24 '19

That's a great question, and i'm not sure what the best approach is here. My intuition tells me that
the API response doesn't require an interface, but rather the model/object you create from the API response should be typed. The reason I say this is that you don't have control over fields the API returns, but you do have control over the properties on the model/object that you create from the API response.

Hopefully that wasn't too abstract of an answer and that it made sense.

Tomek Buszewski • Jan 24 '19

Hey Robert, and thanks for your answer.

While I agree with you, when I create a model, I need to know on which fields I can operate. This is a very common problem for me recently as I work with a lot of CMS' and integrate them into our app via modeling.

Ben Calder • Sep 12 '19

You do of course need to type what you expect to get in the response and then use within your application. In my experience any unused data needn't be typed...

But this is one situation where IMO typings can give a false sense of security: API responses that are out of your control can (and often will) change unexpectedly - e.g. return null on a property where you don't expect it; so it's still important to have some guards in place to avoid responses that might crash your application.

Eugene Karataev • Apr 5 '20

Thanks for the great article!
I'm new to TypeScript and couple of days ago I decided to convert my Node JS project to TS for better maintability. I heard many times that firts steps should be painless - just rename .js to .ts.

TypeScript allows you to easily convert a JavaScript file by changing the file extension from .js to .ts and all the code will compile properly as TypeScript.

Nevertheless, I faced couple of problems from the beginning.
Consider the most basic Node project:

// hello.ts
function hello() {
  console.log('hello');
}

module.exports = {
  hello
};

// index.ts
const {hello} = require('./hello');

hello();

JS version works as expected, but TS throws

error TS2451: Cannot redeclare block-scoped variable 'hello'.

I had to replace require to import across all project files to fix the issue.

Another problem popped up when I tried to compile TS files without types for 3rd party libraries.

Anyway, right now I'm in the middle of moving the project to TS and I feel much more confident with it's logic and data structures compared to the raw JS version.

G. • Jan 20 '19 • Edited

Is there a type that corresponds to () => any? Is it interchangeable with Function?

Paul Cook • Jan 21 '19

You could type a function like that:

function foo(): () => any {
  return 'bar';
}

I generally avoid using the any type, so, in that case I would type it like so:

function foo(): () => string {
  return 'bar';
}

Same goes for arguments.

I see many gifted devs default to any a lot when they're first getting into TypeScript. I think that is fine as a start, but as a goal I would want to have the proper types for arguments/return values.

I think a heavy use of any generally indicates a lack of clarity about your program, and if you have a lack of clarity than anyone who works on the code after you will be even more unclear.

Why don't you know what the types are? And how can you better figure them out?

Sagar Bhattacharya • Apr 29 '19

Good Point , whenever we are writing code we should be very sure of the input and output , which leads to clarity of logic as well as a good code-base , simple to read and simple to extend. When I started coding I was very poor about making this decision , but overtime I have learned that even if you cannot adhere to strict types in early phase , you must make sure to correct those things in self-review and make it a part of the code writing to be very clear about all the possible input and outputs.

Robert Cooper • Jan 21 '19 • Edited

Good question. There is no function type. When annotating types for a function, you must specify the types of the parameters and the return values.

Ant • Jan 24 '19

really great,I can't wait to use Typescript after reading your article.

Jan Wedel • Jan 27 '19

Hi, great summary! Thanks for writing, I will keep it in my bookmarks.

Vladimir Varbanov • Jan 27 '19

great introduction - many thanks!

Richard C • Jan 22 '19

Excellent summary. I just started with typescript a couple weeks ago and am enjoying working with it. I may refer back to this as "quick reference". ;)

Çağatay Sert • Aug 24 '19

Thanks a lot. It was very helpful article for me :))

Mochamad Faishal Amir • Apr 3 '19

Hi Robert this article very helpful, I learn Angular and also must have knowledge about Typescript.

Varma Bhupatiraju • Oct 15 '19

Nice intro to TypeScript. Thank you.

Antonio • Feb 20 '19

Very good article, thanks for sharing.
Do you have any tips regarding debugging in TS?

Robert Cooper • Feb 20 '19

Debugging TS errors can sometimes be tricky since they are not always straightforward. However, the more you work with TS, the more better you'll get interpreting the errors.