Typescript async method declaration

Question

What is the difference between :

public myFunction = async (
    req: Request, 
    res: Response
): Promise<Response> => {
    return await myOtherFunction() 
}

and

public async myFunction (
    req: Request, 
    res: Response
): Promise<Response> {
   return await myOtherFunction()
}

I mostly use the first exemple, but when converting a function that is not async, my code editor (vs code) uses the second exemple.

Probably not relevant but I am using typescript 3.1.3

Jimi Pajala · Accepted Answer · 2018-10-20 22:04:04Z

1

First one is an arrow function and second one is called normal function.

Main difference is that arrow functions this refers to an parent object/class and normal functions this refers to an function itself. If you would use arrow function in node and use it on top level it would refer to undefined.

reference code, heres little reference code which is made in React.js, just to demonstrate the use case.

edited Oct 20, 2018 at 22:04

answered Oct 20, 2018 at 21:56

Jimi Pajala

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6 Comments

L. Faros Over a year ago

According to your links, the first one is a normal function and the second one is an arrow function no ?

Jimi Pajala Over a year ago

My bad I miss spelled it. It is actually other way around, I fix it to the answer. Good notice!

L. Faros Over a year ago

Thank you very much, I didn't quite get the difference (not using the this keyword a lot) but your answer totally explains what I was wondering about

Jimi Pajala Over a year ago

Just to make things more clear I also added example of top level arrow function to codesandbox example.

Jimi Pajala Over a year ago

Some frameworks like React.js uses this-keyword a lot so you'll get use to them if you get into one of these frameworks. Otherwise it doesn't affect too much which of these functions you are using.

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