JavaScript instanceof和moment.js [英] JavaScript instanceof and moment.js

问题描述

我试图了解JavaScript世界中的类型.我的页面正在使用 moment.js .我有一个函数，有时返回一个moment()，有时返回一个string(它的遗留代码变得疯狂了).

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).

我的代码看起来像这样:

My code kind of looks like this:

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;
}

当我执行上面的代码时，我从没得到we have a moment..即使我手动进行设置result = moment();.这是为什么?我是误解了instanceof还是moment?

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 instanceof or moment?

推荐答案

首先，instanceof并不是十分可靠.

First of all, instanceof isn't perfectly reliable.

所有第二个，moment()返回未公开给用户的Moment类的实例.以下代码证明了这一点:

Second of all, moment() returns instance of Moment class that isn't exposed to user. Following code prove this:

moment().__proto__.constructor // function Moment()
moment().constructor === moment; // false

第三，moment提供功能moment.isMoment将解决您的问题.

Third of all, moment provide function moment.isMoment that will solve your problem.

最后，但并非最不重要的一点-您的代码应使用一致的返回类型-始终返回moment实例或始终返回字符串.将来会减轻您的痛苦.

And last, but not least - your code should use consistent return types - always return moment instances or always return strings. It will reduce your pain in future.

您可以通过调用moment函数来确保始终拥有moment实例-moment(string)等于值moment(moment(string))，因此您始终可以将参数转换为moment实例.

You can ensure that you always have moment instance by calling moment function - moment(string) equals in value moment(moment(string)), so you can just always convert your argument to moment instance.

这篇关于JavaScript instanceof和moment.js的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！