如何对数组或函数使用可选链接? [英] How to use optional chaining with array or functions?

问题描述

我正在尝试对数组而不是对象使用可选链接，但不知道该怎么做:

I'm trying to use optional chaining with an array instead of an object but not sure how to do that:

这就是我想要做的myArray.filter(x => x.testKey === myTestKey)?[0].还用函数尝试类似的事情:

Here's what I'm trying to do myArray.filter(x => x.testKey === myTestKey)?[0]. Also trying similar thing with a function:

let x = {a: () => {}, b: null}
console.log(x?b());

但是它给出了这样的错误，所以如何将它与数组或函数一起使用.

But it's giving an error like that so how to use it with an array or a function.

推荐答案

你需要在 ? 后面放一个 . 才能使用可选链:

You need to put a . after the ? to use optional chaining:

myArray.filter(x => x.testKey === myTestKey)?.[0]

游乐场链接

仅使用 ? 会使编译器认为您正在尝试使用条件运算符(然后它会抛出错误，因为它没有看到 :稍后)

Using just the ? alone makes the compiler think you're trying to use the conditional operator (and then it throws an error since it doesn't see a : later)

可选链不仅仅是 TypeScript 的东西 - 它是一个完成的提案 在纯 JavaScript 中 也是如此.

Optional chaining isn't just a TypeScript thing - it is a finished proposal in plain JavaScript too.

它可以与上面的括号表示法一起使用，但也可以与点表示法属性访问一起使用:

It can be used with bracket notation like above, but it can also be used with dot notation property access:

const obj = {
  prop2: {
    nested2: 'val2'
  }
};

console.log(
  obj.prop1?.nested1,
  obj.prop2?.nested2
);

还有函数调用:

const obj = {
  fn2: () => console.log('fn2 running')
};

obj.fn1?.();
obj.fn2?.();

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