Makes mod editing only send changed data (#286)

* Add getDifferences lib

* Only send mod diff to backend for changes

* Disable fields when lacking permissions

libs/getDifferences.js

@@ -0,0 +1,23 @@
+const equalArrays = (arr1, arr2) =>
+  arr1.length === arr2.length &&
+  arr1.every((element, index) => element === arr2[index])
+
+const isObject = (obj) => obj instanceof Object && !Array.isArray(obj)
+
+const isArray = (arr) => Array.isArray(arr)
+
+export default function getDifferences(obj1, obj2) {
+  const obj3 = {}
+  for (const key of Object.keys(obj1)) {
+    const val1 = obj1[key]
+    const val2 = obj2[key]
+    const areArrays = isArray(val1) && isArray(val2)
+    const areObjects = isObject(val1) && isObject(val2)
+    if (areObjects) {
+      const diff = getDifferences(val1, val2)
+      if (diff) obj3[key] = diff
+    } else if (areArrays && !equalArrays(val1, val2)) obj3[key] = val2
+    else if (val1 !== val2) obj3[key] = val2
+  }
+  return !!Object.keys(obj3).length && obj3
+}