Javascript date variable assignment

问题

var date1 = new Date();  
date1.setFullYear(2011, 6, 1);  

// 2011-07-01, ok  
console.log(date1);

// set date2 the same date as date1  
var date2 = date1;

// ...

// now I'm gonna set a new date for date2  
date2.setFullYear(2011, 9, 8);

// 2011-10-08, ok  
console.log(date2);

// 2011-10-08, wrong, expecting 2011-07-01  
// I didn't assign a new date to date1  
// WHY is date1 changed?  
console.log(date1);

回答1:

Date is object , so it is assigned as reference - simple approach is

date2 = new Date( date1 );

回答2:

Both date variables are just references to the same date object in memory. So you need date2 to be a clone of date1. Change:

var date2 = date1;

to this:

var date2 = new Date(date1.getTime());

回答3:

date2 It's a reference to date1.

To achieve the expected results, do the following:

var date1 = new Date();
date1.setFullYear(2011, 6, 1); 

var date2 = new Date();
date2.setTime(date1.valueOf());

回答4:

JavaScript uses pass by reference for Dates* (as well as all non-primitives -- var o = {}; var j = o; j.foo = 1; console.log(o.foo); //1. On the other hand, for Numbers, Strings, and Booleans var o = 0; var j = o; j++; console.log(j); // 0), so that is expected behavior.

If you need to copy a date you can always

var date2 = new Date( date1.getTime() );

* Please see comments to understand why this is not entirely correct.

回答5:

You need to create a copy of date1, currently date1 and date2 refer to the same date object.

var date2 = new Date(date1.valueOf());

回答6:

Variation of @SergeS's answer, but Date() objects in js coerce to number, so you don't need getTime():

// general case
var dateValueCopy = new Date(date1);

And restated with OP variable names:

var date2 = new Date(date1);

回答7:

<html lang="en">
<head>
<script>
function getDateDiff(time1, time2) {
var str1= time1.split('/');
var str2= time2.split('/');
var t1 = new Date(str1[2], str1[0]-1, str1[1]);
var t2 = new Date(str2[2], str2[0]-1, str2[1]);

var diffMS = t1 - t2;    
console.log(diffMS + ' ms');

var diffS = diffMS / 1000;    
console.log(diffS + ' ');

var diffM = diffS / 60;
console.log(diffM + ' minutes');

var diffH = diffM / 60;
console.log(diffH + ' hours');

var diffD = diffH / 24;
console.log(diffD + ' days');
alert(diffD);
}

//alert(getDateDiff('10/18/2013','10/14/2013'));
</script>
</head>
<body>
<input type="button" onclick="getDateDiff('10/18/2013','10/14/2013')" value="clickHere()" />
</body>
</html>

来源：https://stackoverflow.com/questions/6609574/javascript-date-variable-assignment

标签

javascript

variables

date