instantsearch.js implementation (still not working)

src/functions/mergePure.js

@@ -1,16 +1,34 @@
 'use strict';
 
-module.exports = require('lodash/merge');
+const uniq = require('lodash/uniq');
+
+// NOTE: repeated because #656 isn't merged yet
+function objectHasKeys(obj) {
+  return Object.keys(Object(obj)) > -1;
+}
 
 // NOTE: this behaves like lodash/merge, but doesn't mutate the target
-// module.exports = function defaultsPure() {
-//   const sources = Array.prototype.slice.call(arguments);
-//   return sources.reduceRight(function(acc, source) {
-//     Object.keys(Object(source)).forEach(function(key) {
-//       if (source[key] !== undefined) {
-//         acc[key] = source[key];
-//       }
-//     });
-//     return acc;
-//   }, {});
-// };
+module.exports = function mergeDeep() {
+  var values = Array.prototype.slice.call(arguments);
+  return values.reduce(function(acc, source) {
+    source = source || {};
+    Object.keys(Object(source)).forEach(function(key) {
+      var previousValue = acc[key];
+      var nextValue = source[key];
+
+      if (Array.isArray(previousValue)) {
+        var nextArray = Array.isArray(nextValue) ? nextValue : [nextValue];
+        acc[key] = uniq([].concat(previousValue, nextArray));
+      } else if (objectHasKeys(nextValue)) {
+        acc[key] = mergeDeep(previousValue, nextValue);
+      } else {
+        acc[key] = nextValue;
+      }
+    });
+
+    return acc;
+  }, {});
+};
+
+// TODO: make this removable
+module.exports = require('lodash/merge');