numberFormat callback to format numbers

README.md

@@ -223,6 +223,28 @@ polyglot.t("car", 2);
 => "2 cars"
 ```
 
+If you pass a `numberFormat` _function_ to the constructor, Polyglot will use
+it to translate interpolated `Number`s to `String`s. That's useful because
+different locales have different rules for formatting numbers: `2,000.56` in
+English versus `1 234,56` in French, for instance.
+
+```js
+polyglot = new Polyglot({
+  phrases: { num_cars: '%{smart_count} car |||| %{smart_count} cars' },
+  numberFormat: new Intl.NumberFormat('en').format // Chrome, Firefox, IE11+, Node 0.12+ with ICU
+})
+polyglot.t("num_cars", 2000); // internally, calls options.numberFormat.format(2000)
+=> "2,000 cars"
+```
+
+(A primer on [Intl.NumberFormat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NumberFormat)
+in Node: Node 0.12+ comes with Intl as long as it's compiled with ICU (which is
+the default). By default, the only locale Node supports is en-US. You can add
+[full-icu](https://www.npmjs.com/package/full-icu) to your project to support
+other locales. Finally, Polyglot accepts a _function_, not an Intl.NumberFormat
+instance: if you have a NumberFormat instance, pass its `.format` property to
+Polyglot.
+
 If you like, you can provide a default value in case the phrase is missing.
 Use the special option key "_" to specify a default.
 

index.js

@@ -171,7 +171,7 @@ var defaultTokenRegex = /%\{(.*?)\}/g;
 //
 // You should pass in a third argument, the locale, to specify the correct plural type.
 // It defaults to `'en'` with 2 plural forms.
-function transformPhrase(phrase, substitutions, locale, tokenRegex) {
+function transformPhrase(phrase, substitutions, locale, tokenRegex, numberFormat) {
   if (typeof phrase !== 'string') {
     throw new TypeError('Polyglot.transformPhrase expects argument #1 to be string');
   }
@@ -197,8 +197,14 @@ function transformPhrase(phrase, substitutions, locale, tokenRegex) {
   // Interpolate: Creates a `RegExp` object for each interpolation placeholder.
   result = replace.call(result, interpolationRegex, function (expression, argument) {
     if (!has(options, argument) || options[argument] == null) { return expression; }
+
+    var replacement = options[argument];
+    if (typeof replacement === 'number' && typeof numberFormat === 'function') {
+      replacement = numberFormat(replacement);
+    }
+
     // Ensure replacement value is escaped to prevent special $-prefixed regex replace tokens.
-    return replace.call(options[argument], dollarRegex, dollarBillsYall);
+    return replace.call(replacement, dollarRegex, dollarBillsYall);
   });
 
   return result;
@@ -214,6 +220,7 @@ function Polyglot(options) {
   this.onMissingKey = typeof opts.onMissingKey === 'function' ? opts.onMissingKey : allowMissing;
   this.warn = opts.warn || warn;
   this.tokenRegex = constructTokenRegex(opts.interpolation);
+  this.numberFormat = opts.numberFormat || String;
 }
 
 // ### polyglot.locale([locale])
@@ -370,7 +377,7 @@ Polyglot.prototype.t = function (key, options) {
     result = key;
   }
   if (typeof phrase === 'string') {
-    result = transformPhrase(phrase, opts, this.currentLocale, this.tokenRegex);
+    result = transformPhrase(phrase, opts, this.currentLocale, this.tokenRegex, this.numberFormat);
   }
   return result;
 };

test/index.js

@@ -9,7 +9,8 @@ describe('t', function () {
     hello: 'Hello',
     hi_name_welcome_to_place: 'Hi, %{name}, welcome to %{place}!',
     name_your_name_is_name: '%{name}, your name is %{name}!',
-    empty_string: ''
+    empty_string: '',
+    number: '%{number}'
   };
 
   var polyglot;
@@ -156,6 +157,16 @@ describe('t', function () {
       instance.t(missingKey);
     });
   });
+
+  it('uses numberFormat', function () {
+    var instance = new Polyglot({
+      phrases: phrases,
+      // prove we're passed a Number by doing math on it and formatting it
+      numberFormat: function (n) { return 'x' + (n + 2); }
+    });
+
+    expect(instance.t('number', { number: 1234.56 })).to.equal('x1236.56');
+  });
 });
 
 describe('pluralize', function () {