Sort dates not returned Sort dates

Question

For some strange reason, the following function that I wrote to convert an array of date strings to javascript date objects, sort them, and then return an array of sorted date strings is not sorted properly:

sortdates: function(dates, separator) { var sorteddates = [], datestr =[]; sorteddates = dates.map(function(val) { return new Date(val.replace("/"+separator+"/g", " ")); }).sort(); for ( i=0; i<sorteddates.length; i++ ) { datestr.push((sorteddates[i].getMonth()+1) + "-" + sorteddates[i].getDate() + "-" + sorteddates[i].getFullYear()); } return datestr; } 

If I create a test array of date strings and apply this function:

 var testarray = ["2013-8-1", "2013-8-8", "2013-8-15", "2013-8-22", "2013-9-5", "2013-9-12", "2013-8-2", "2013-8-3", "2013-8-4", "2013-8-7", "2013-8-11", "2013-8-14", "2013-8-18", "2013-8-25"]; console.log(sortdates(testarray, "-")); 

I get the following entries to the console:

 ["8-2-2013", "8-3-2013", "8-4-2013", "8-11-2013", "8-18-2013", "8-25-2013", "8-1-2013", "8-8-2013", "8-15-2013", "8-22-2013", "9-5-2013", "9-12-2013", "8-7-2013", "8-14-2013"] 

Clearly not sorted.

Answer 1

.sort() will be sorted in dictionary order, not digitally or by date / time. If the values ​​are not strings, they will get the default string conversion, which for dates does not give you anything useful for sorting.

But you can provide a custom callback that knows how to sort dates:

 .sort(function(a,b) { return a.getTime() - b.getTime(); }); 

Demo: http://jsfiddle.net/TUAz9/

Answer 2

sort() will be sorted based on the string representation of the entries in the array. In this case, the string representation of the date looks like Thu Aug 01 2013 00:00:00 GMT-0700 (PDT) , so the main view will be in alphabetical order by day of the week.

 Fri Aug 02 2013 00:00:00 GMT-0700 (PDT) Sat Aug 03 2013 00:00:00 GMT-0700 (PDT) Sun Aug 04 2013 00:00:00 GMT-0700 (PDT) Sun Aug 11 2013 00:00:00 GMT-0700 (PDT) Sun Aug 18 2013 00:00:00 GMT-0700 (PDT) Sun Aug 25 2013 00:00:00 GMT-0700 (PDT) Thu Aug 01 2013 00:00:00 GMT-0700 (PDT) Thu Aug 08 2013 00:00:00 GMT-0700 (PDT) Thu Aug 15 2013 00:00:00 GMT-0700 (PDT) Thu Aug 22 2013 00:00:00 GMT-0700 (PDT) Thu Sep 05 2013 00:00:00 GMT-0700 (PDT) Thu Sep 12 2013 00:00:00 GMT-0700 (PDT) Wed Aug 07 2013 00:00:00 GMT-0700 (PDT) Wed Aug 14 2013 00:00:00 GMT-0700 (PDT) 

You'll probably want to take a look at using a custom sort callback function or some other date representation — maybe start by matching the array with the timestamp value instead of the Date object?

 return new Date(/* stuff */).getTime(); 

... along with corresponding changes to the formatting code later in your function.

Combining all this, such a function will work as you expect:

 sortdates: function(dates, separator) { return dates.map(function(val) { return new Date(val.replace("/"+separator+"/g", " ")).getTime(); }).sort().map(function(val) { var d = new Date(val); return (d.getMonth()+1) + "-" + d.getDate() + "-" + d.getFullYear(); }); }