Errors: Deprecated toLocaleFormat

The JavaScript warning "Date.prototype.toLocaleFormat is deprecated; consider using Intl.DateTimeFormat instead" occurs when the non-standard Date.prototype.toLocaleFormat method is used.


Warning: Date.prototype.toLocaleFormat is deprecated; consider using Intl.DateTimeFormat instead

Error type

Warning. JavaScript execution won't be halted.

What went wrong?

The non-standard Date.prototype.toLocaleFormat method is deprecated and shouldn't be used anymore. It uses a format string in the same format expected by the strftime() function in C. The function is no longer available in Firefox 58+.


Deprecated syntax

The Date.prototype.toLocaleFormat method is deprecated and will be removed (no cross-browser support, available in Firefox only).

var today = new Date(); 
var date = today.toLocaleFormat('%A, %e. %B %Y');

// In German locale
// "Freitag, 10. März 2017"

Alternative standard syntax using the ECMAScript Intl API

The ECMA-402 (ECMAScript Intl API) standard specifies standard objects and methods that enable language sensitive date and time formatting (available in Chrome 24+, Firefox 29+, IE11+, Safari10+).

You can now either use the Date.prototype.toLocaleDateString method if you just want to format one date.

var today = new Date();
var options = { weekday: 'long', year: 'numeric',
                month: 'long', day: 'numeric' };
var date = today.toLocaleDateString('de-DE', options);

// "Freitag, 10. März 2017"

Or, you can make use of the Intl.DateTimeFormat object, which allows you to cache an object with most of the computations done so that formatting is fast. This is useful if you have a loop of dates to format.

var options = { weekday: 'long', year: 'numeric', 
                month: 'long', day: 'numeric' }; 
var dateFormatter = new Intl.DateTimeFormat('de-DE', options)

var dates = [Date.UTC(2012, 11, 20, 3, 0, 0), 
             Date.UTC(2014, 04, 12, 8, 0, 0)]; 

dates.forEach(date => console.log(dateFormatter.format(date)));

// "Donnerstag, 20. Dezember 2012"
// "Montag, 12. Mai 2014"

Alternative standard syntax using Date methods

The Date object offers several methods to build a custom date string.

(new Date()).toLocaleFormat("%Y%m%d");
// "20170310"

Can be converted to:

let now = new Date();
let date = now.getFullYear() * 10000 + 
          (now.getMonth() + 1) * 100 + now.getDate();

// "20170310"

See also

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