如何从字符串日期数组中获取最大日期字符串？

Question

What would be the most elegant way to get max date from an array of strings like below?

var dates = ["2018-12-29T15:23:20.486695Z", "2018-12-29T15:23:21.613216Z", "2018-12-29T15:23:22.695710Z", "2018-12-29T15:23:24.013567Z", "2018-12-29T15:23:25.097649Z", "2018-12-29T15:23:26.692125Z", "2018-12-29T15:23:27.918561Z", "2018-12-29T15:23:29.217879Z", "2018-12-29T15:23:30.468284Z", "2018-12-29T15:23:31.548761Z"]

I have tried:

var timestamps = dates.map(date => Date.parse(date));
var max_date = Math.max.apply(Math, timestamps)

But this leaves me with a timestamp that I would need to convert back to the exact original format (and I don't know how to do that).​

Answer 1

You could compare the ISO 8601 date like strings and take the greater value.

 var dates = ["2018-12-29T15:23:20.486695Z", "2018-12-29T15:23:21.613216Z", "2018-12-29T15:23:22.695710Z", "2018-12-29T15:23:24.013567Z", "2018-12-29T15:23:25.097649Z", "2018-12-29T15:23:26.692125Z", "2018-12-29T15:23:27.918561Z", "2018-12-29T15:23:29.217879Z", "2018-12-29T15:23:30.468284Z", "2018-12-29T15:23:31.548761Z"], latest = dates.reduce((a, b) => a > b ? a : b); console.log(latest);

Answer 2

That's the format provided by toISOString on Date . So you take your timestamp value, feed it into new Date , and use toISOString on the result:

console.log(new Date(max_date).toISOString());

Example:

 var dates = [ "2018-12-29T15:23:20.486695Z", "2018-12-29T15:23:21.613216Z", "2018-12-29T15:23:22.695710Z", "2018-12-29T15:23:24.013567Z", "2018-12-29T15:23:25.097649Z", "2018-12-29T15:23:26.692125Z", "2018-12-29T15:23:27.918561Z", "2018-12-29T15:23:29.217879Z", "2018-12-29T15:23:30.468284Z", "2018-12-29T15:23:31.548761Z" ]; var timestamps = dates.map(date => Date.parse(date)); var max_date = Math.max.apply(Math, timestamps) console.log(new Date(max_date).toISOString());

Note that you get "2018-12-29T15:23:31.548Z" rather than "2018-12-29T15:23:31.548761Z" because you've parsed the strings to JavaScript dates, and JavaScript dates only hold milliseconds, not microseconds.