refactor the whole damn thing

src/Type/YMap.js

@@ -0,0 +1,32 @@
+import Type from '../Struct/Type'
+import Item from '../Struct/Item'
+import ItemJSON from '../Struct/ItemJSON'
+
+export default class YMap extends Type {
+  set (key, value) {
+    let old = this._map.get(key)
+    let v
+    if (value instanceof Item) {
+      v = value
+    } else {
+      let v = new ItemJSON()
+      v._content = JSON.stringify(value)
+    }
+    v._right = old
+    v._parent = this
+    v._parentSub = key
+    v._integrate()
+  }
+  get (key) {
+    let v = this._map.get(key)
+    if (v instanceof Type) {
+      return v
+    } else {
+      return v._content[v._content.length - 1]
+    }
+  }
+  _logString () {
+    let s = super._logString()
+    return 'YMap: ' + s
+  }
+}