reimplement persistence approach

src/Util/simpleDiff.js

@@ -0,0 +1,19 @@
+
+export default function simpleDiff (a, b) {
+  let left = 0 // number of same characters counting from left
+  let right = 0 // number of same characters counting from right
+  while (left < a.length && left < b.length && a[left] === b[left]) {
+    left++
+  }
+  if (left !== a.length || left !== b.length) {
+    // Only check right if a !== b
+    while (right + left < a.length && right + left < b.length && a[a.length - right - 1] === b[b.length - right - 1]) {
+      right++
+    }
+  }
+  return {
+    pos: left,
+    remove: a.length - left - right,
+    insert: b.slice(left, b.length - right)
+  }
+}