问题
In Javascript certain operators are processed before others:
1 + 2 * 3
// 1 + (2 * 3)
// 7 because * has higher precedence than +
1 === 0 + 1
// 1 === (0 + 1)
// true because + has a higher precedence than ===
The MDN has a full breakdown of all operators and their precedence ... except await.
await getFoo() * 2; // await (getFoo() * 2) or (await getFoo()) * 2?
await getFoo() === 5; // await (getFoo() === 5) or (await getFoo()) === 5?
Can anyone explain which operators are processed before/after await?
Right now I feel like I have to add a bunch of parenthesis that are probably unnecessary because I'm not sure what will get handled before/after await. And while I know I should just be able to look this up, even MDN (the gold standard of documentation IMHO) doesn't have the answer.
回答1:
An AwaitExpression is an UnaryExpression and has the same precedence as delete, void, typeof, +, -, ~, and !, binding stronger than any binary operator.
This is unlike yield which has a precedence lower than anything else except the comma operator. This design decision was made because both yield a+b and await a + await b are scenarios thought to be more common than (yield a) + (yield b) and await (a + b).
来源：https://stackoverflow.com/questions/48218744/what-is-the-operator-precedence-of-await