Use a Function, not a NumberFormat

README.md

@@ -243,15 +243,15 @@ polyglot.t("car", 2);
 => "2 cars"
 ```
 
-If you pass a `numberFormat` to the constructor, interpolated `Number`s will
-be formatted by its `format()` method. 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.
+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') // Chrome, Firefox, IE11+, Node 0.12+ with ICU
+  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"
@@ -261,7 +261,9 @@ polyglot.t("num_cars", 2000); // internally, calls options.numberFormat.format(2
 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.
+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

@@ -147,7 +147,7 @@ function transformPhrase(phrase, substitutions, locale, numberFormat) {
 
     var replacement = options[argument];
     if (typeof replacement === 'number') {
-      replacement = numberFormat.format(replacement);
+      replacement = numberFormat(replacement);
     }
 
     // Ensure replacement value is escaped to prevent special $-prefixed regex replace tokens.
@@ -163,7 +163,7 @@ function Polyglot(options) {
   this.phrases = {};
   this.extend(opts.phrases || {});
   this.currentLocale = opts.locale || 'en';
-  this.numberFormat = opts.numberFormat || { format: String };
+  this.numberFormat = opts.numberFormat || String;
   this.allowMissing = !!opts.allowMissing;
   this.warn = opts.warn || warn;
 }

package.json

@@ -6,7 +6,7 @@
   "scripts": {
     "pretest": "npm run --silent lint",
     "test": "npm run --silent tests-only",
-    "tests-only": "NODE_ICU_DATA=node_modules/full-icu mocha test/*.js --reporter spec",
+    "tests-only": "mocha test/*.js --reporter spec",
     "lint": "eslint *.js test/*.js",
     "docs": "docco -o docs/ index.js"
   },

test/index.js

@@ -91,11 +91,11 @@ describe('t', function () {
     expect(instance.t('header.sign_in')).to.equal('Sign In');
   });
 
-  it('uses an Intl.NumberFormat', function () {
+  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: { format: function (n) { return 'x' + (n + 2); } }
+      numberFormat: function (n) { return 'x' + (n + 2); }
     });
 
     expect(instance.t('number', { number: 1234.56 })).to.equal('x1236.56');