Round a timestamp to the nearest date

问题:

I need to group a bunch of items in my web app by date created.

Each item has an exact timestamp, e.g. 1417628530199. I'm using Moment.js and its "time from now" feature to convert these raw timestamps into nice readable dates, e.g. 2 Days Ago. I then want to use the readable date as a header for a group of items created on the same date.

The problem is that the raw timestamps are too specific - two items that are created on the same date but a minute apart will each have a unique timestamp. So I get a header for 2 Days Ago with the first item underneath, then another header for 2 Days Ago with the second item underneath, etc.

What's the best way to round the raw timestamps to the nearest date, so that any items created on the same date will have the exact same timestamp and thus can be grouped together?

回答1:

Try this:

Date.prototype.formatDate = function() {
   var yyyy = this.getFullYear().toString();
   var mm = (this.getMonth()+1).toString();
   var dd  = this.getDate().toString();
   return yyyy + (mm[1]?mm:"0"+mm[0]) + (dd[1]?dd:"0"+dd[0]);
  };

var utcSeconds = 1417903843000,
    d = new Date(0);

d.setUTCSeconds(Math.round( utcSeconds / 1000.0));

var myTime = (function(){
        var theTime = moment(d.formatDate(), 'YYYYMMDD').startOf('day').fromNow();
        if(theTime.match('hours ago')){
            return 'Today';
        }
        return theTime;
    })();

alert( myTime );

http://jsfiddle.net/cdn5rvck/4/

回答2:

Well, using js you can do:

var d = new Date(1417628530199);
d.setHours(0);
d.setMinutes(0);
d.setSeconds(0);
d.setMilliseconds(0);

Edit:

After checking several methods, this one seems to be the faster:

function roundDate(timeStamp){
    timeStamp -= timeStamp % (24 * 60 * 60 * 1000);//subtract amount of time since midnight
    timeStamp += new Date().getTimezoneOffset() * 60 * 1000;//add on the timezone offset
    return new Date(timeStamp);
}

You can check difference in speed here: http://jsfiddle.net/juvian/3aqmhn2h/

回答3:

Using Moment.js, you can use the following code to round everything to the beginning of the day:

moment().startOf('day').toString();
// -> Prints out "Fri Dec 05 2014 00:00:00 GMT-0800"

You can read more about startOf() in the docs.

回答4:

Just construct a new Date from the existing one using only the year, month, and date.

var now = new Date(Date.now());
var round = new Date(now.getFullYear(),now.getMonth(),now.getDate());
console.log(now);
console.log(round);

Since this seems to have a small footprint, it can also be useful to extend the prototype to include it in the Date "class".

Date.prototype.round = function(){
    var dateObj = new Date(+this);
    return new Date(dateObj.getFullYear(), dateObj.getMonth(), dateObj.getDate());
};
console.log(new Date().round());

Minimized:

Date.prototype.round = function(){var d = new Date(+this);return new Date(d.getFullYear(), d.getMonth(), d.getDate());};

回答5:

function roundDownDate(date) {
  if (typeof date !== "object" || !date.getUTCMilliseconds) {
      throw Error("Arg must be a Date object.");
  }
  var offsetMs = date.getTimezoneOffset() * 60 * 1000,
      oneDayMs = 24 * 60 * 60 * 1000;
  return new Date(Math.floor((date.getTime() - offsetMs) / oneDayMs) * oneDayMs + offsetMs);
};

This should work and is pretty fast.

回答6:

function getDateOfTimeStamp(time) {
  var originTime = 0;
  var offsetOriginTime = originTime + new Date().getTimezoneOffset() * 60 * 1000;
  var timeSinceOrigin = time - offsetOriginTime;
  var timeModulo = timeSinceOrigin % (24 * 60 * 60 * 1000);
  var normalizedTime = time - timeModulo;

  console.log(new Date(normalizedTime) ,new Date(time));
  return normalizedTime;
}

This worked for my project. Pure math, no string manipulation needed, no external lib needed, so it's super fast.

You can try by copying the above function to javascript console and then do normalizeTimeToDate(Date.now())