CODEWITHSUNDEEP
javascript
John Winston
John Winston

Reputation: 1471

How to write a one line callback arrow function to throw error?

How can I write this simple callback with arrow function?

(error) => {
  throw error
}

The following doesn't work:

(error) => throw error

Upvotes: 0

Views: 1367

Answers (2)

Humayoun_Kabir
Humayoun_Kabir

Reputation: 2251

If you don't use a block like {} as body of an arrow function , the body must be an expression. Like if you use

(error) => throw error

is equivalent to

(error) => { return throw error; }

throw is a statement not expression , that's why it is not valid. So you have to define like below:

(error) => {throw error};

Upvotes: 2

CertainPerformance
CertainPerformance

Reputation: 370699

throw is a statement (something that does something), and not an expression (which evaluates to a value).

When using concise body syntax - an arrow function without a { following => - what follows the => must be an expression. So, (error) => throw error doesn't work - your only option is to put the throw in the context of somewhere where an expression is permitted, which will have to be inside a block:

(error) => {
  throw error
}

You can put it all on one line if you want, but the brackets will still be required:

(error) => { throw error }

I suppose you could use a concise body for the outer function and put in an IIFE which makes a new block, inside of which throw will be permitted, but that adds syntax noise for no real gain IMO:

(error) => (() => { throw error })();

Throw expressions are at stage 2. Eventually, it may well be possible to use throw like you want, with a concise body - but it's not possible quite yet.

Upvotes: 4

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