Resolve #140

README.md

@@ -118,7 +118,7 @@ Expand all edges in the graph.
 Load elements from JSON string.
 
 `api.saveJson(elems, filename)`
-Saves elements in JSON format to a file. Default value for `elems` is all the elements. Default value for `filename` is 'expand-collapse-output.json'
+Return elements in JSON format and saves them to a file if a file name is provided via `filename` parameter. Default value for `elems` is all the elements.
 
 ## Events
 Notice that following events are performed for *each* node that is collapsed/expanded. Also, notice that any post-processing layout is performed *after* the event.

demo/demo-compounds.js

@@ -492,7 +492,7 @@ function main() {
   });
 
   document.getElementById('saveAsJson').addEventListener('click', function () {
-    api.saveJson(cy.$());
+    api.saveJson(cy.$(), 'expand-collapse-output.json');
   });
 
   document.getElementById('loadFromJson').addEventListener('click', function () {

src/index.js

@@ -368,7 +368,7 @@
       };
 
       api.saveJson = function (elems, filename) {
-        saveLoadUtils.saveJson(elems, filename);
+        return saveLoadUtils.saveJson(elems, filename);
       };
 
       return api; // Return the API instance

src/saveLoadUtilities.js

@@ -256,10 +256,11 @@ function saveLoadUtilities(cy, api) {
         o.nodes.push(jsonObj);
       }
 
-      if (!filename) {
-        filename = 'expand-collapse-output.json';
+      let stringifiedJSON = JSON.stringify(o);
+      if (filename) {
+        str2file(stringifiedJSON, filename);
       }
-      str2file(JSON.stringify(o), filename);
+      return stringifiedJSON;
     }
   };
 }