Javascript colon (:) operator inside function

Question

I apologize if this question is stupid or duplicated, please point me to the right direction if so.

I've tested this code:

function b()
{
    a: 22;
    return a;
}

Code returns no error. Which leads me into thinking a: 20 inside function works. Though when call the function:

b();

..I receive "ReferenceError: a is not defined"

What does a: 22 inside function actually do? this.a inside function returns nothing so I don't think it has something to do with function as object (or it does?..)

Does this answer your question? What does ':' (colon) do in JavaScript? — 0stone0
– 0stone0, Commented Apr 9, 2020 at 15:15
a: 22 is a label: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… — Daniel Diekmeier
– Daniel Diekmeier, Commented Apr 9, 2020 at 15:15
@DanielDiekmeier never heard of labels in javascript. Thanks! Do post as answer to mark it — user8555937
– user8555937, Commented Apr 9, 2020 at 15:17
@user8555937 Please take a look at the second aswer which explains the label style as @Daniel explains — 0stone0
– 0stone0, Commented Apr 9, 2020 at 15:18

Daniel Diekmeier · Accepted Answer · 2020-04-09 15:22:36Z

2

The a: 22 in your code is a label – it labels the statement 22 with the identifier a.

From MDN:

The labeled statement can be used with break or continue statements. It is prefixing a statement with an identifier which you can refer to.

Read more here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label

answered Apr 9, 2020 at 15:22

Daniel Diekmeier

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