从客户端的对象数组中获取最新日期的优雅方法是什么？

A clean way to do it would be to convert each date to a Date() and take the max

ES6:

new Date(Math.max(...a.map(e => new Date(e.MeasureDate))));

JS:

new Date(Math.max.apply(null, a.map(function(e) {
return new Date(e.MeasureDate);
})));

where a is the array of objects.

What this does is map each of the objects in the array to a date created with the value of MeasureDate. This mapped array is then applied to the Math.max function to get the latest date and the result is converted to a date.

By mapping the string dates to JS Date objects, you end up using a solution like Min/Max of dates in an array?

--

A less clean solution would be to simply map the objects to the value of MeasureDate and sort the array of strings. This only works because of the particular date format you are using.

a.map(function(e) { return e.MeasureDate; }).sort().reverse()[0]

If performance is a concern, you may want to reduce the array to get the maximum instead of using sort and reverse.

function getLatestDate(data) {
// convert to timestamp and sort
var sorted_ms = data.map(function(item) {
return new Date(item.MeasureDate).getTime()
}).sort();
// take latest
var latest_ms = sorted_ms[sorted_ms.length-1];
// convert to js date object
return new Date(latest_ms);
}


var data = [{MeasureDate: "2014-10-04T16:10:00"},
{MeasureDate: "2013-10-04T16:10:00"},
{MeasureDate: "2012-10-04T16:10:00"}];


getLatestDate(data).toString(); // "Sat Oct 04 2014 18:10:00 GMT+0200 (CEST)"

This function returns the latest date as a JavaScript date Object. You can also turn it into an ISO-String (the format of your source data) with the Date-Object method toISOString().

var date_str = "2012-10-04T16:10:00";
(new Date(date_str)).toISOString(); // "2012-10-04T16:10:00.000Z"

As you can see the result of the method includes always zero milliseconds in the end. If you need your original ISO data-string as a result, you may want to go with the following function:

function getLatestDate2(data) {


var sorted = data.map(function(item) {
var MeasureDate = item.MeasureDate;
return {original_str: MeasureDate,
in_ms: (new Date(MeasureDate)).getTime()}
}).sort(function(item1, item2) {
return (item1.in_ms < item2.in_ms)
});


// take latest
var latest = sorted[0];


return latest.original_str;
}


getLatestDate2(data); // "2014-10-04T16:10:00"

Inspired by many of the suggestions and comments in this thread, here is another solution for the problem. It's very fast, since there is no date object convertion.

function getLatestDate(xs) {
if (xs.length) {
return xs.reduce((m, i) => (i.MeasureDate > m) && i || m, "")
.MeasureDate;
}
}

Here's a version for Browser's not supporting arrow functions:

function getLatestDateSave(xs) {
if (xs.length) {
return xs.reduce(function(m, i) {
return (i.MeasureDate > m) && i || m;
}, "").MeasureDate;
}
}

Modification to Anton Harald's answer: The array I have uses ModDate instead of MeasureDate. I am choosing the most recent date. This works.

  getLatestDate(xs) {
if (xs.length) {
return xs.reduce((m,v,i) => (v.ModDate > m.ModDate) && i ? v : m).ModDate;
}
}

m = accumulator, v = current , i = index

Environment: TypeScript, ES6

If you want to get the whole Object, not just the date...

If OP's array of Objects was assigned to a this is how you get the Object with the most recent date:

var mostRecentDate = new Date(Math.max.apply(null, a.map( e => {
return new Date(e.MeasureDate);
})));
var mostRecentObject = a.filter( e => {
var d = new Date( e.MeasureDate );
return d.getTime() == mostRecentDate.getTime();
})[0];

1. a.map gets the dates from the array of objects.
2. new Date is applied to each date, making Date Objects
3. Math.max.apply finds the most recent
4. We have found the most recent Date, now we need the object.
5. a.filter loops through the original a array.
6. We need some way to compare dates, so we use .getTime(), which returns the number of milliseconds since 01/01/1970. This will account for time - if it's defined - as well as date.
7. When the correct date is found, true is returned, and .filter gives us just that object.

Note: This solution is an extension of @archyqwerty's answer above. Their solution gave only the most recent date from an array of objects, this solution gives you the whole Object that the date was a member of.

Further to @Travis Heeter's answer, this returns the object that contains the latest date:

array.reduce((a, b) => (a.MeasureDate > b.MeasureDate ? a : b));

A more robust solution perhaps might be convert the strings into Date objects every time. Could be noticeably slower if dealing with (very) large arrays:

array.reduce((a, b) => {
return new Date(a.MeasureDate) > new Date(b.MeasureDate) ? a : b;
});

        var dates = [];


dates.push(new Date("2019/06/25"));
dates.push(new Date("2019/06/26"));
dates.push(new Date("2019/06/27"));
dates.push(new Date("2019/06/28"));


function GFG_Fun() {
var maximumDate=new Date(Math.max.apply(null, dates));
var minimumDate=new Date(Math.min.apply(null, dates));
}

Also further to @TravisHeeter's answer..

Instead of using 'filter' and grabbing the array index of [0], you can use the .find() method instead as follows:

....


const mostRecentObject = a.find( e => {
const d = new Date( e.MeasureDate );
return d.getTime() == mostRecentDate.getTime();
});

This also makes the code more performant, as it will stop looking after it has found the result, rather than filter which will iterate over all objects in the array.

This how I picked lasest/highest date

var maxLastseen= obj.sort((a,b) => new Date(b.lastS).getTime() - new Date(a.lastS).getTime())[0];

Answers rated by performance:

1. data.reduce((a, b) => a.MeasureDate > b.MeasureDate ? a : b).MeasureDate
2. data.map(e => e.MeasureDate).reduce((a, b) => a > b ? a : b)
3. new Date(Math.max.apply(null, data.map(e => new Date(e.MeasureDate)))).toISOString()

(assuming x is the array)

By this, you can get the whole object - I just clubbed the process which I learned from Travis Heeter's answer:

let latestDate = Math.max(...a.map((ele) => new Date(ele.dof)));
latestDate = new Date(latestDate);
console.log(latestDate);


let latestObject = a.filter((ele) => {
let date = new Date(ele.dof);
return date.getTime() === latestDate.getTime();
});