normalizing unicode before transliteration

lib/speakingurl.js

@@ -1418,6 +1418,8 @@
 
     var markChars = ['.', '!', '~', '*', "'", '(', ')'].join('');
 
+    var isNormalizeFeaturePresent = typeof ''.normalize === 'function';
+
     /**
      * getSlug
      * @param  {string} input input string
@@ -1529,6 +1531,11 @@
         // escape all necessary chars
         allowedChars = escapeChars(allowedChars);
 
+        // normalize unicode chars
+        if (isNormalizeFeaturePresent) {
+            input = input.normalize('NFC');
+        }
+
         // trim whitespaces
         input = input.replace(/(^\s+|\s+$)/g, '');
 
@@ -1686,4 +1693,4 @@
             }
         } catch (e) {}
     }
-})(this);
+})(this);

test/test-unicode-normalization.js

@@ -0,0 +1,22 @@
+/* global describe,it */
+
+var getSlug = require('../lib/speakingurl');
+
+describe('getSlug unicode normalization', function () {
+    'use strict';
+
+    it('should normalize unicode before applying transformations', function (done) {
+        // given
+        var wordWithUmlautCanonical = 'klärung';
+        var wordWithUmlautCombined = 'kla\u0308rung';
+
+        // when
+        var slugifiedCanonical = getSlug(wordWithUmlautCanonical);
+        var slugifiedCombined = getSlug(wordWithUmlautCombined);
+
+        // expect
+        getSlug(slugifiedCanonical).should.eql(slugifiedCombined);
+
+        done();
+    });
+});