How to get ISO8601-presentation for date using ICU-string in javascript?

Question

Are there a robust and crutch-less way to print Date inside the ICU-message string, using ISO-8601 format - YYYY-MM-DDThh:mm:ss?

Subquestion 1: are other custom format string supported?

Subquestion 2: why Intl.DateTimeFormat doesn't support custom formatting?

Details and observations

I want to use ICU-messages for i18n features for the javascript application. There are at least two packages on NPM, allowing to format message-strings:

• intl-messageformat
• format-message

Each has some kind of formatMessageFunction, accepting the raw ICU-message, the name of locale and data for applying. But both uses Intl.DateTimeFormat (looks, like it is the industry standard):

• Proof for Intl-Messageformat
• Proof for format-message

and it can't format dates using custom format.

Despite the described limitations of mentioned implementations, the ICU describes a way of custom formatting for dates

Example

My ICU-string:

var icu_string = `Hello,
    <strong>{username}</strong>,
    it is
    <time datetime="{ts, date, ???}">{ts, date}</time>
    `;

Sample code:

var IntlMessageFormat = require('intl-messageformat'); // no matter, which NPM package to use
var formatter = new IntlMessageFormat(icu_string, 'en');
var output = formatter.format({
    username: 'Barack Obama',
    ts: new Date()
});
console.log(output);

The desirable output is Hello, <strong>Barack Obama</strong>, it is <time datetime="2016-10-25T01:01:15Z">Oct 25, 2016</time>

You could test current behavior here: format-message.github.io

Similar questions

• question about ISO and ICU. But I don't want to play with locale parameter (the code will use the selected locale for translation).

Answer 1

A simple workaround is to pass in the timestamp pre-formatted. At least for ISO timestamps, you can pass date.toISOString() as a separate parameter to the message.

var IntlMessageFormat = require('intl-messageformat'); // no matter, which NPM package to use
var icu_string = 'Hello, {username}, it is {ts, date} (ISO-timestamp  is {tsiso})'
var formatter = new IntlMessageFormat(icu_string, 'en');
var date = new Date();
var output = formatter.format({
    username: 'Barack Obama',
    ts: date,
    tsiso: date.toISOString()
});
console.log(output);

Both intl-messageformat and format-message have a way to define a custom format, based however on Intl.DateTimeFormat options, instead of ICU's SimpleDateFormat.

Answer 2

Take a look at closure, goog.i18n.DateTimeFormat: https://google.github.io/closure-library/api/goog.i18n.DateTimeFormat.html

It uses a subset of the ICU patterns (in the above link click "VIEW SOURCE", and see doc from line 33)

Warning: using your own pattern means you become responsible to "get it right", as you throw away the stuff that the library "knows" about the proper locale formatting.

What are you trying to achieve that the intl stuff doesn't support?