JavaScript instanceof 和 moment.js
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JavaScript instanceof and moment.js
提问by Some User
I'm attempting to understand types in the JavaScript world. My page is using moment.js. I have a function that sometimes returns a moment()and other times, returns a string(it's legacy code gone wild).
我试图理解 JavaScript 世界中的类型。我的页面正在使用moment.js。我有一个功能，有时会返回一个moment()等次，返回string（它的遗留代码狂野）。
My code kind of looks like this:
我的代码看起来像这样：
var now = getDate();
if (now instanceof moment) {
console.log('we have a moment.');
} else {
console.log('we have a string.');
}
function getDate() {
var result = null;
// Sometimes result will be a moment(), other times, result will be a string.
result = moment();
return result;
}
When I execute the code above, I never get we have a moment.. Even if I manually make set result = moment();. Why is that? Am I misunderstanding instanceofor moment?
当我执行上面的代码时，我从来没有得到we have a moment.. 即使我手动设置 set result = moment();。这是为什么？是我误会了instanceof还是moment？
回答by FreeLightman
Moment version 2.13.0
时刻版本 2.13.0
There is a static method .isMoment:
有一个静态方法.isMoment：
回答by Ginden
First of all, instanceofisn't perfectly reliable.
首先，instanceof不是完全可靠的。
Second of all, moment()returns instance of Momentclass that isn't exposed to user. Following code prove this:
其次，moment()返回Moment未向用户公开的类的实例。下面的代码证明了这一点：
moment().__proto__.constructor // function Moment()
moment().constructor === moment; // false
Third of all, momentprovide function moment.isMomentthat will solve your problem.
第三，moment提供moment.isMoment可以解决您问题的功能。
And last, but not least - your code should use consistent return types - always return momentinstances or always return strings. It will reduce your pain in future.
最后但并非最不重要的 - 您的代码应该使用一致的返回类型 - 始终返回moment实例或始终返回字符串。它会减少你未来的痛苦。
You can ensure that you always have momentinstance by calling momentfunction - moment(string)equals in value moment(moment(string)), so you can just always convert your argument to momentinstance.
您可以moment通过调用momentfunction - moment(string)equals in value来确保您始终拥有实例moment(moment(string))，因此您可以始终将参数转换为moment实例。
