Why is it when I write {}.key = 0
in the chrome console I get an error:
> {}.key = 0
> Uncaught SyntaxError: Unexpected token .
But when I encapsulate the above expression in parentheses (( )
) I get no error:
> ({}.key = 0)
> 0
What exactly is going on here? I would have thought the same error I got in the first scenario still applied to the second?
Image of console output:
{ }
are overloaded in JavaScript syntax. They're used for both blocks (of statements) and object literals. The rule is: If a {
appears at the start of a statement, it is parsed as a block; otherwise it is an object literal.
In {}.key
the {
appears at the start of the statement. It parses as
{
// this is an empty block
}
.key // syntax error here
Adding any token before {
(such as (
) makes it parse as an object literal. For example, 42, {}.key = 0
would also work.
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