feat: multi srcset, close #5

Author: Scrum

lib/index.js

@@ -64,10 +64,18 @@ function getPicture (imgNode, options) {
   imgNode.skip = true
 
   var src = imgNode.attrs.src
-  if (options.replaceExtension) {
-    src = removeExtension(src)
-  }
-  src += '.webp'
+  var srcset = (imgNode.attrs.srcset || '')
+    .split(',')
+    .concat(src)
+    .filter(Boolean)
+    .map(value => {
+      value = value.trim().split(/\s/)
+      var path = options.replaceExtension ? removeExtension(value[0]) : value[0]
+      var size = value[1]
+
+      return [path + '.webp', size].filter(Boolean).join(' ')
+    })
+    .join(', ')
 
   return {
     tag: 'picture',
@@ -76,7 +84,7 @@ function getPicture (imgNode, options) {
         tag: 'source',
         attrs: {
           type: 'image/webp',
-          srcset: src
+          srcset
         }
       },
       imgNode