Javascript中的日期变量问题 [英] issue with date variable in Javascript

问题描述

var dt_from = "2013/05/25";
var dt_to   = "2013/05/25";

if(dt_from == dt_to)
{
    alert("Both dates are Equal!");
}
else if(dt_from > dt_to)
{
    alert("From date should not be greater than todate!");
}
else if(dt_from < dt_to)
{
    alert("Okay!");
}

上述代码工作正常。但以下代码无效：

The above Code is working fine. But the following code is not working:

var dt_from = new Date("2013/05/25");
var dt_to   = new Date("2013/05/25");

if(dt_from === dt_to)
{
    alert("Both dates are Equal!");
}
else if(dt_from > dt_to)
{
    alert("From date should not be greater than todate!");
}
else if(dt_from < dt_to)
{
    alert("Okay!");
}

此 if（dt_from === dt_to）无法使用上述代码。任何想法？

This if(dt_from === dt_to) is not working with the above code. Any Idea?

推荐答案

您正在将对象引用与 == 进行比较。虽然它们可能代表相同的日期时间，但它们是不同的对象。使用< / > 可以将对象转换为数字（自纪元以来的毫秒数），然后进行比较。如果要测试相等性，则必须手动强制转换：

You are comparing object references with ==. While they may represent the same datetime, they are distinct objects. Using </> works as it casts the objects to numbers (milliseconds since epoch) which are then compared. If you want to test on equality, you have to force that conversion manually:

dt_from.getTime() == dt_to.getTime() // most explicit
// or
+dt_from == +dt_to // shortest
dt_from - dt_to == 0  // equivalent…
dt_from.valueOf() == dt_to.valueOf()
Number(dt_from) == Number(dt_from)

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