Export a typescript function or a typescript const reference to a function?

Question

I'm new to typescript and I am questioning a pattern in the codebase I inherited:

export const registerTubesReducer = handleTubeActions

function handleTubeActions(previousState: ITubes, action: TubeAction): ITubes {

versus

export function registerTubesReducer(previousState: ITubes, action: TubeAction): ITubes {

Is there any reason other than style to prefer export const over the plain function export?

Possible duplicate of Arrow function vs function declaration / expressions: Are they equivalent / exchangeable? — Lionel Tay
– Lionel Tay, Commented Oct 11, 2018 at 2:24
function & arrow functions treat "this" differently. If you are aware of that then not much to add. I would say the first snipped is bad though because it uses "handleTubeActions" before it is defined. — Catalyst
– Catalyst, Commented Oct 11, 2018 at 2:27

Lionel Tay · Accepted Answer · 2018-10-11 02:23:09Z

There is no major difference in this case. Although the first version can be simplified to

export const registerTubesReducer = (previousState: ITubes, action: TubeAction): ITubes => { ... }

Differences to be aware of between arrow and regular functions.

1) Arrow functions have a lexically bound this which does not change depending on how you invoke the function

2) Arrow functions are not hoisted as they are just variable declarations with a function value. You will not be able to use the function until it is defined or else you will be calling and undefined variable

arrowAdd(1, 2) // arrowAdd will be undefined here
functionAdd(1,2) // All good since function declarations are hoisted

const arrowAdd = (a: number, b: number) => a + b

function functionAdd(a: number, b:number) {
  return a + b
}

3) Arrow functions allow you to omit the extra curly braces if you only want to return a value

There is a canonical answer here for more details about the differences between arrow and regular functions

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