Moment.js incorrect formatting

user_14045027 0
Viewed 189

Moment suddenly started to format dates incorrectly. Like, completely changing them. I don't understand why. I made a short video so you can see what's going on here: https://youtu.be/WPLDiiWsfAo

Here's some of the code that's working wrong:

activeProject() {
  let proj = { ...this.$store.state.activeProject };
  if (proj.Start) {
    debugger;
    proj.Start = moment(proj.Start).format("MM/DD/YYYY");
    proj.End = moment(proj.End).subtract(1, "days").format("MM/DD/YYYY");
    return proj;
  } else return {};
},

proj.Start = "2021-03-01T00:00:00.000Z" outputs 02/28/2021
proj.End = "2021-03-08T00:00:00.000Z" outputs 03/06/2021

So after formatting with moment, it takes 1 days off of proj.Start and proj.End. Why would it be doing this?

momentjs javascript
1 Answers

In the ISO 8601 standard, the Z means UTC (Coordinated Universal Time), which in practice is London, England Time.

Your issue is reproduced below if you are in a timezone west of London, England (like me) and the current time time in London just passed 00:00 (like right now as I write this answer). That snippet would ouput the right values for one being in a timezone East of London, at the same moment.

let proj = {Start: "2021-03-01T00:00:00.000Z", End:"2021-03-08T00:00:00.000Z"}

proj.Start = moment(proj.Start).format("MM/DD/YYYY");
proj.End = moment(proj.End).subtract(1, "days").format("MM/DD/YYYY");

console.log(proj.Start, "expected: 03/01/2021")
console.log(proj.End, "expected: 03/07/2021")
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>

Notice without the Z now...

let proj = {Start: "2021-03-01T00:00:00.000", End:"2021-03-08T00:00:00.000"}

proj.Start = moment(proj.Start).format("MM/DD/YYYY");
proj.End = moment(proj.End).subtract(1, "days").format("MM/DD/YYYY");

console.log(proj.Start, "expected: 03/01/2021")
console.log(proj.End, "expected: 03/07/2021")
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>

So your issue is specififying a date/time relative to UTC while it seems it is not what you want.

Your solution would be to remove the final Z from the data used...

moment(...) is local mode. Ambiguous input (without offset) is assumed to be local time. Unambiguous input (with offset) is adjusted to local time.

Moment documentation

user_21595280
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