provide fix for bug related to parsing GET parameters (#832)

* provide fix for bug related to parsing GET parameters

* expand to test for a path that has already escaped the query string

Author: kyle-mccarthy

js/core.js

@@ -233,9 +233,13 @@ proto.updateGetPathTemplate = function( optPath ) {
   }.bind( this );
   // get pageIndex from location
   // convert path option into regex to look for pattern in location
-  var regexString = optPath.replace( '{{#}}', '(\\d\\d?\\d?)' );
+  // escape query (?) in url, allows for parsing GET parameters 
+  var regexString = optPath
+    .replace(/(?<!\\)\?/, '\\?')
+    .replace( '{{#}}', '(\\d\\d?\\d?)' );
   var templateRe = new RegExp( regexString );
   var match = location.href.match( templateRe );
+
   if ( match ) {
     this.pageIndex = parseInt( match[1], 10 );
     this.log( 'pageIndex', [ this.pageIndex, 'template string' ] );

test/unit/page-index.js

@@ -26,4 +26,29 @@ QUnit.test( 'pageIndex', function( assert ) {
 
   history.replaceState( null, document.title, prevURL );
 
+  infScroll.destroy();
+
+  history.replaceState(null, document.title, 'page?currPage=8');
+  infScroll = new InfiniteScroll( demoElem, {
+    path: 'page?currPage={{#}}',
+    history: false,
+    scrollThreshold: false,
+  });
+
+  assert.equal( infScroll.pageIndex, 8, 'pageIndex from GET param with {{#}}' );
+
+  history.replaceState( null, document.title, prevURL );
+
+  infScroll.destroy();
+
+  history.replaceState(null, document.title, 'page?currPage=8');
+  infScroll = new InfiniteScroll( demoElem, {
+    path: 'page\\?currPage={{#}}',
+    history: false,
+    scrollThreshold: false,
+  });
+
+  assert.equal( infScroll.pageIndex, 8, 'pageIndex from GET param with {{#}} and pre-escaped regexp' );
+
+  history.replaceState( null, document.title, prevURL );
 });