Javascript getTime() returns different time than time object itself

Question

Javascript getTime() returns different time than time object itself.

function doTime(){
  var data = [];
  var newDate = new Date('2020-01-01');

  for (var i = 0; i < 10; i++) {
    newDate.setTime(newDate.getTime() + (1000 * 60 * 60));
    console.log(newDate);                //<<----these times are not the same for some reason, why?
    data.push({'date': newDate});        //<<----these times are not the same for some reason, why?
    }
  console.log(data);
  }

And the output!!

Wed Jan 01 2020 03:00:00 GMT+0200 (Eastern European Standard Time)
Wed Jan 01 2020 04:00:00 GMT+0200 (Eastern European Standard Time)
Wed Jan 01 2020 05:00:00 GMT+0200 (Eastern European Standard Time)
Wed Jan 01 2020 06:00:00 GMT+0200 (Eastern European Standard Time)
Wed Jan 01 2020 07:00:00 GMT+0200 (Eastern European Standard Time)
................

(10) [{…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}, {…}]
0: {date: Wed Jan 01 2020 12:00:00 GMT+0200 (Eastern European Standard Time)}
1: {date: Wed Jan 01 2020 12:00:00 GMT+0200 (Eastern European Standard Time)}
2: {date: Wed Jan 01 2020 12:00:00 GMT+0200 (Eastern European Standard Time)}
3: {date: Wed Jan 01 2020 12:00:00 GMT+0200 (Eastern European Standard Time)}
4: {date: Wed Jan 01 2020 12:00:00 GMT+0200 (Eastern European Standard Time)}
................

btw I already solved this problem with a slightly different code, but can someone please explain why is this happening?

The array has 5 references to the same Date object: `data[0] === data[1] === data[2] ...`. Use `data.push({'date': new Date(newDate)})`. — RobG, Sep 29 '20 at 00:25

score 6 · Accepted Answer · edited Oct 17 '20 at 08:59

6

You aren't creating a new reference in your loop, so you are mutating the same newDate each time. You are also calling console.log so at that time, it's converted to its console format.

edited Oct 17 '20 at 08:59

halfer

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answered Sep 28 '20 at 22:25

Daniel A. White

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Javascript getTime() returns different time than time object itself

1 Answers1