let b = 10
x: a = b
b // 10
a // 10
x // Uncaught ReferenceError: x is not definedWhat is x and how a exists without declaring it first?
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3[Labelled statements](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/label) – Pointy May 31 '19 at 09:29
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2`a` *does* exist, you assigned to it with `a=b` – CertainPerformance May 31 '19 at 09:29
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2`a` is implicit global. – Maheer Ali May 31 '19 at 09:29
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1As it stands how OP shows it, it is invalid syntax. – connexo May 31 '19 at 09:30
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it's not invalid syntax in chrome. maybe in other browsers, it is. – Stav Alfi May 31 '19 at 09:33
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@connexo no it is not invalid; try it. Any statement can be labelled. – Pointy May 31 '19 at 09:37
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@Pointy Run it in latest Firefox. `"message": "ReferenceError: x is not defined",` – connexo May 31 '19 at 09:44
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@connexo sure, that's an error because in fact `x` is not defined as a variable of any kind. The label part, which I think was the point of the question, is fine however. (Pointless, but syntactically correct.) – Pointy May 31 '19 at 09:57