Parse time string and convert it into a date object in Javascript

Question

I want to create a Date object in TypeScript (AngularJS) from this string: 08:00:00.000+01:00 in order to use a filter in the end to show only the hour and the minute:

.filter('toDate', () => {
    return input => {
        let date = Date.parse(input);
        return date;
    }
})

In the HTML:

{{ object.unformatedTimeString | toDate | date: 'H:m' }}

Does anyone know a good way how to parse such a time string?

Why don't you just pull the hour and minute from the string? let [hr, min] = str.split(':');. Why the conversion? — Jared Smith
– Jared Smith, Commented Mar 27, 2018 at 18:56
Because there is also timezone information in the time string. Better convert it correctly. — nimrod
– nimrod, Commented Mar 27, 2018 at 18:57
Have you considered using moment.js? It is much more versatile than javascripts date object. — Igor
– Igor, Commented Mar 27, 2018 at 18:58
@Igor it's also massive and complex. Worth it if you have a lot of date manipulations, but not necessarily for small stuff. — Jared Smith
– Jared Smith, Commented Mar 27, 2018 at 19:00
moment.js would be an option if it integrates nicely into AngularJS (1.6.x). — nimrod
– nimrod, Commented Mar 27, 2018 at 19:04

Jared Smith · Accepted Answer · 2018-03-27 19:15:22Z

2

Let [ts, tz] = str.split(/[\+\-]/);
let [hr, min] = ts.split(':').map(Number);
let offsetSign = str.includes('+') ? 1 : -1;
let [offsetHr, offsetMin] = tz.split(':');
let offset = offsetSign * ((offsetHr * 1000 * 60 * 60) + (offsetMin * 1000 * 60));

let date = new Date();
date.setHour(hr);
date.setMinute(min);
let result = new Date(date.getTime() + offset);

Tedious, but not complex or difficult.

answered Mar 27, 2018 at 19:15

Jared Smith

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1 Comment

RobG Over a year ago

There's no need to convert [hr, min] to Number as multiplication will convert them as required and you should do date.setHour(hr, min, 0, 0) to set the time in one go. This may return a Date before the current date, the OP should test thoroughly to ensure the logic is correct, it may need to set UTC hour and minute. ;-)

RobG · Accepted Answer · 2018-03-27 23:11:22Z

1

One solution is to adjust the time for the timezone, making it a UTC time, then apply it to the current UTC date, e.g.

function parseToUTCTime(s) {
  var now = new Date();
  var b = s.match(/\d+|\D/g);
  var sign = b[7]=='+'? 1 : -1;
  now.setUTCHours(+b[0] + sign*b[8], +b[2] + sign*b[10], 0, 0);
  return now;
}

// Tests
['08:00:00.000+01:00',
 '06:30:00.000-08:00',
 '04:15:00.000+05:30'].forEach(ts =>
   console.log(ts + ' -> ' + parseToUTCTime(ts).toISOString())
 );

answered Mar 27, 2018 at 23:11

RobG

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