Why is a semicolon needed here? [duplicate]

问题

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Destructuring assignment in while loop in ES6 function doesn't propogate out of loop? (1 answer)

Closed 4 years ago.

I am simply using es6 to reassign variables a & b. Why do I get an error if I leave the semicolon off of the a and b declaration and assignment statements? Does the parser try to pull a property out of 2 if the semicolon is left off? let b = 2[a, b]...?

Works:
let a = 1;
let b = 2;
[a, b] = [b, a]

Error:

let a = 1
let b = 2
[a, b] = [b, a]

I am looking for the actual reason this fails. Thanks!

回答1:

Does the parser try to pull a property out of 2 if the semicolon is left off? let b = 2[a, b]...?

Yes. You cannot safely start a statement with a [ if you're not explicitly ending statements with semicolons.

This has been written about in many places, and it's one of the many things that standardJS (or other linters) will warn you about: http://standardjs.com/rules.html#semicolons

来源：https://stackoverflow.com/questions/39753755/why-is-a-semicolon-needed-here