是否可以在javascript中检查null内联? [英] Is it possible to check for null inline in javascript?

问题描述

我有一个函数，可以解析Google Maps API JSON 的地址部分，然后返回城市/地区/路线名称.

I have a function which parses the address components of the Google Maps API JSON and then returns the city / locality / route name.

getAddressComponent()如果找不到密钥，则返回 null .

The getAddressComponent() returns a null if it cannot find the key.

让route = getAddressComponent(addressComponents，'route').value.long_name;

因此，假设它没有找到密钥，然后我得到一个 Error:TypeError:显然因为未定义，所以无法读取未定义的属性'long_name'.

So let's say it didn't find the key, then I get a Error: TypeError: Cannot read property 'long_name' of undefined obviously because it's not defined.

除了条件方法(a === null)之外，如何在javascript中检查 null ?

How do I check for null in javascript other than the conditional method (a === null)?

如何简单地通过进行这样的检查?

安全导航操作员

让route = getAddressComponent(addressComponents，'route')?. value.long_name;

如果不存在，则可能将 route 设置为 null ，而不是抛出错误?

And if it doesn't exists, it could probably set route to null instead of throwing a Error ?

推荐答案

2020年答案，存在！！

您现在可以直接使用?.内联测试是否存在.它被称为 Optional Chaining Operator (可选的链接运算符)，所有现代浏览器均支持该功能.

2020 Answer, It Exists!!!

You can now directly use ?. inline to test for existence. It is called the Optional Chaining Operator, supported by all modern browsers.

如果存在一个属性，它将继续进行下一个检查，或返回该值.任何故障都会立即短路并返回 undefined .

If a property exists, it proceeds to the next check, or returns the value. Any failure will immediately short-circuit and return undefined.

const example = {a: ["first", {b:3}, false]}

example?.a  // ["first", {b:3}, false]
example?.b  // undefined

example?.a?.[0]     // "first"
example?.a?.[1]?.a  // undefined
example?.a?.[1]?.b  // 3

domElement?.parentElement?.children?.[3]?.nextElementSibling

要确保默认定义的值，可以使用 ?? .如果需要第一个真实值，则可以使用 || .

To ensure a default defined value, you can use ??. If you require the first truthy value, you can use ||.

example?.c ?? "c"  // "c"
example?.c || "c"  // "c"

example?.a?.[2] ?? 2  // false
example?.a?.[2] || 2  // 2

如果不检查大小写，则必须存在left-side属性.如果没有，它将引发异常.

If you do not check a case, the left-side property must exist. If not, it will throw an exception.

example?.First         // undefined
example?.First.Second  // Uncaught TypeError: Cannot read property 'Second' of undefined

?.浏览器支持-2021年3月89％

?. Browser Support - 89%, Mar 2021

?? 浏览器支持-89％

?? Browser Support - 89%

节点支持-v14 +

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