How this arrow function doesn't give any error?

Question

I just run up into some code and then I did a test and found something I don't understand.

hey(
  () => {},
  () => {
    foo: "bar";
  }
);

Why the following syntax is a valid syntax? In the first argument, I can understand, because is an empty function scope, but in the second argument, how it doesn't give me an error?

If it's returning a object, it should be ({...}) and don't accept ; at the end, so this means that the second argument isn't an object.

If it isn't an object, what is it? Why it isn't a syntax error?

What black javascript magic is happening here?

Here is an example on codesanbox and it doens't give me any syntax error.

Edit

I just found some other weird thing.

hey(
  () => {},
  () => {
    "bar"; // without foo:
  }
);

How this doesn't give any error?

after your edit: why would that give an error? You're allowed to have a string that doesn't do anything. It's meaningless, but no reason to error — TKoL, Dec 18 '19 at 14:00

score 5 · Accepted Answer · answered Dec 18 '19 at 14:00

5

If you skip the (), it's interpreted as a labeled statement

() => {
  foo: "bar";
}

If add another property, you can see the error clearly

() => {
  foo: "bar",
  baz: ''
}

answered Dec 18 '19 at 14:00

adiga

34,372
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TKoL · Answer 2 · 2019-12-18T13:57:46.750

-2

The second argument ISN'T an object. It's a function. The second argument is basically equivalent to saying

function() {
   foo: "bar";
}

Which in fact doesn't error, despite looking like it should

If you want an arrow function to return an object immediately, the syntax is

() => ({foo:'bar'})

edited Dec 18 '19 at 13:57

answered Dec 18 '19 at 13:56

TKoL

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What is that? How can it do `foo: "bar";` without any error? – Vencovsky Dec 18 '19 at 13:57
@Vencovsky no idea, I think it's meaningless but not an error. – TKoL Dec 18 '19 at 13:58
@Vencovsky I edited my answer to show how you'd return an object from an arrow function – TKoL Dec 18 '19 at 13:58
2

well.. that doesn't explain much – Vencovsky Dec 18 '19 at 14:00

How this arrow function doesn't give any error?

Edit

2 Answers2