这个 JavaScript 表达式是什么意思？

Question

我正在使用 react-navigation，但我无法理解此语法的含义。

React.useEffect(() => {
    if (route.params?.post) { <<<<<WHAT IS THIS ?
      // Post updated, do something with `route.params.post`
      // For example, send the post to the server
    }
  }, [route.params?.post]);

它是否像 obect.doesPropertyExist.subProperty 或其他东西一样工作？

我已尝试浏览 MDN 文档，但找不到对此类语法的任何参考。我无法在我的节点 REPL 中对随机对象使用类似的语法。

Answer 1

叫做Optional Chaining operator。 shorthand

route.params && route.params.post

Answer 2

它被称为可选链接。 MDN 文档中提供：

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining

The optional chaining operator (?.) permits reading the value of a property located deep within a chain of connected objects without having to expressly validate that each reference in the chain is valid. The ?. operator functions similarly to the . chaining operator, except that instead of causing an error if a reference is nullish (null or undefined), the expression short-circuits with a return value of undefined. When used with function calls, it returns undefined if the given function does not exist.

if(route.params.post) 然后做点什么。它检查 route.params 是否有对象 post

这个 JavaScript 表达式是什么意思？

What does this JavaScript expression mean?

javascript

syntax

node.js

react-navigation