Adds truncate filter.

Author: addyosmani

demo.html

@@ -24,6 +24,9 @@ <h3>reverse</h3>
     <h3>replace('World','Peeps')</h3>
     {{'Hello World' | replace('World','Peeps')}}
 
+    <h3>truncate(8, true)</h3>
+    {{'Lorem Catsum Itsum' | truncate(8, true) }}
+
     <h3>startsWith(T)</h3>
     <template repeat="{{friend in friends | startsWith('T')}}">
         {{ friend.name }}
@@ -83,15 +86,20 @@ <h3>trim</h3>
 	template.colors = ['red','green','blue','yellow'];
 	template.greeting = 'Hello World';
 	template.friends = [{
-	    name: 'Matt'        
+	    name: 'Matt',
+        dinner: 'pizza'       
 	  }, {
-	    name: 'Paul'
+	    name: 'Paul',
+        dinner: 'sushi'
 	  }, {
-	    name: 'Eric'
+	    name: 'Eric',
+        dinner: 'hummus'
 	  }, {
-	    name: 'Rob'
+	    name: 'Rob',
+        dinner: 'burger'
 	  }, {
-	    name: 'Timothy'
+	    name: 'Timothy',
+        dinner: 'pasta'
 	  }];
   </script>
 </body>

filter-truncate.js

@@ -0,0 +1,29 @@
+/**
+ * Return a truncated version of a string
+ * @param  {string} input     
+ * @param  {integer} length   
+ * @param  {boolean} killwords 
+ * @param  {string} end       
+ * @return {string}           
+ */
+PolymerExpressions.prototype.truncate = function (input, length, killwords, end) {
+    var orig = input;
+    length = length || 255;
+
+    if (input.length <= length)
+        return input;
+
+    if (killwords) {
+        input = input.substring(0, length);
+    } else {
+        var idx = input.lastIndexOf(' ', length);
+        if (idx === -1) {
+            idx = length;
+        }
+
+        input = input.substring(0, idx);
+    }
+
+    input += (end !== undefined && end !== null) ? end : '...';
+    return input;
+};

polymer-filters.html

@@ -11,6 +11,7 @@
 <script src="filter-wordcount.js"></script>
 <script src="filter-random.js"></script>
 <script src="filter-round.js"></script>
+<script src="filter-truncate.js"></script>
 <script src="filter-trim.js"></script>
 
 <!--
@@ -48,6 +49,20 @@
 
 > I was a string with leading and trailing whitespace
 
+####Truncate
+
+    {{'Lorem Catsum Itsum' | truncate(8) }}
+
+> Lorem...
+
+    {{'Lorem Catsum Itsum' | truncate(8, true) }}
+
+> Lorem Ca...
+
+    {{'Lorem Catsum Itsum' | truncate(8, true, ' [READ MORE]') }}
+
+> Lorem Ca [READ MORE]
+
 ####Date
 
     {{1288323623006 | date('yyyy-MM-dd HH:mm:ss Z')}}
@@ -115,5 +130,6 @@
 @element polymer-filters
 @blurb A collection of Polymer filters for formatting values of expressions for display to users
 @homepage http://addyosmani.github.io/polymer-filters
+@inspiration http://jinja.pocoo.org/docs/templates/
 -->