feat(__): added tagged template literal support

README.md

@@ -23,6 +23,19 @@ output:
 
 `my awesome string foo`
 
+_using tagged template literals_
+
+```js
+var __ = require('y18n').__
+var str = 'foo'
+
+console.log(__`my awesome string ${str}`)
+```
+
+output:
+
+`my awesome string foo`
+
 _pluralization support:_
 
 ```js
@@ -60,6 +73,10 @@ Create an instance of y18n with the config provided, options include:
 
 Print a localized string, `%s` will be replaced with `arg`s.
 
+This function can also be used as a tag for a template literal. You can use it
+like this: <code>__&#96;hello ${'world'}&#96;</code>. This will be equivalent to
+`__('hello %s', 'world')`.
+
 ### y18n.\_\_n(singularString, pluralString, count, arg, arg, arg)
 
 Print a localized string with appropriate pluralization. If `%d` is provided

index.js

@@ -16,6 +16,9 @@ function Y18N (opts) {
 }
 
 Y18N.prototype.__ = function () {
+  if (typeof arguments[0] !== 'string') {
+    return this._taggedLiteral.apply(this, arguments)
+  }
   var args = Array.prototype.slice.call(arguments)
   var str = args.shift()
   var cb = function () {} // start with noop.
@@ -40,6 +43,19 @@ Y18N.prototype.__ = function () {
   return util.format.apply(util, [this.cache[this.locale][str] || str].concat(args))
 }
 
+Y18N.prototype._taggedLiteral = function (parts) {
+  var args = arguments
+  var str = ''
+  parts.forEach(function (part, i) {
+    var arg = args[i + 1]
+    str += part
+    if (arg) {
+      str += '%s'
+    }
+  })
+  return this.__.apply(null, [str].concat([].slice.call(arguments, 1)))
+}
+
 Y18N.prototype._enqueueWrite = function (work) {
   this.writeQueue.push(work)
   if (this.writeQueue.length === 1) this._processWriteQueue()

test/y18n-test.js

@@ -30,6 +30,23 @@ describe('y18n', function () {
   })
 
   describe('__', function () {
+    it('can be used as a tag for template literals', function () {
+      var __ = y18n({ // eslint-disable-line
+        directory: path.join(__dirname, 'locales')
+      }).__
+
+      try {
+        // We need to do this wrapper in case y18n gets used in runtimes
+        // without template literal support.
+        eval('__`Hello ${"Ben"} ${"Coe"}`').should.equal('Hello Ben Coe') // eslint-disable-line
+      } catch (e) {
+        if (e.message.match(/SyntaxError/)) {
+          this.skip()
+        } else {
+          throw e
+        }
+      }
+    })
     it('uses replacements from the default locale if none is configured', function () {
       var __ = y18n({
         directory: path.join(__dirname, 'locales')