问题
In Chrome version ^72 if I run the following JavaScript there are no errors.
{ prop: p } = { prop: 'prop' }
>> { prop: 'prop' }
So the line of code is interpreted as an expression statement, unexpectedly.
But if I run the same code with a semi-colon at the end it runs as expected.
{ prop: p } = { prop: 'prop' };
>> Uncaught SyntaxError: Unexpected token =
This is expected since the initial { tells the JavaScript engine that it is a code block unless we disambiguate with parentheses.
Why does this occur with the semi-colon but not without it?
回答1:
Why does this occur with the semi-colon but not without it?
Chrome uses a very simple test to see whether a line is an object literal or not: Does the line start with a { and end with a }? If yes, the line is evaluated as an expression.
{ prop: p } = { prop: 'prop' } passes that test, but { prop: p } = { prop: 'prop' }; does not.
See Odd behaviour of comparison of object literals for more info (different input, same reason).
来源：https://stackoverflow.com/questions/53712304/why-is-this-javascript-not-interpreted-as-a-code-block-when-semi-colon-is-used