i18next documentation

Formatting
You can define a function to handle formattings. Beside formatting numbers or dates you can use this to define custom formattings.
You can add formatting using moment.js and numeral.js or the intl api.
Basic
As a sample using momentjs to format dates.
keys
{
    "key": "The current date is {{date, MM/DD/YYYY}}",
    "key2": "{{text, uppercase}} just uppercased"
}
Init i18next with a format function:
i18next.init({
    interpolation: {
        format: function(value, format, lng) {
            if (format === 'uppercase') return value.toUpperCase();
            if(value instanceof Date) return moment(value).format(format);
            return value;
        }
    }
});
sample
i18next.t('key', { date: new Date() });
// -> "The current date is 07/13/2016"
​
i18next.t('key2', { text: 'can you hear me' });
// => "CAN YOU HEAR ME just uppercased"
Keep the language on moment in sync with i18next by listening to the change language event:
i18next.on('languageChanged', function(lng) {
  moment.locale(lng);
});
Additional options
Prefix/Suffix for interpolation and other options can be overridden in init option or by passing additional options to t function:
sample
i18next.init({
    interpolation: { ... }
});
​
i18next.t('key', {
    interpolation: { ... }
});
option
default
description
format
noop function
format function function format(value, format, lng) {}
formatSeparator
','
used to separate format from interpolation value
While there are a lot of options going with the defaults should get you covered.

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Contents

Formatting
Basic
Additional options

option	default	description
format	noop function	format function `function format(value, format, lng) {}`
formatSeparator	','	used to separate format from interpolation value