javascript - 可选链接 - Function.prototype.apply 在未定义时调用，这是未定义而不是函数

Question

对函数调用使用可选链会导致表达式自动返回 undefined，而不是在找不到方法时抛出异常。

注意：代码使用的是spread syntax，而不是rest parameters。

const fn1 = undefined
const args = []
const fn2 = () => {}
const fn3 = () => {}

console.log(fn1?.(...args, fn2, fn3))

错误：

console.log(fn1?.(...args, fn2, fn3))
                                ^
TypeError: Function.prototype.apply was called on undefined, which is an undefined and not a function

Answer 1

It turns out to be a V8 bug, I've submitted it there, hopefully, it'll be fixed soon.

Update: it has been fixed.

Answer 2

...rest 参数需要遵循一些规则。

其中一个规则是 ...rest 参数只能是最后一个参数。

foo(...one, ...wrong, ...wrong)
foo(...wrong, bad, bad)
foo(ok, ok, ...correct)

看：

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters