Move Mark-deserializing into Mark.fromJSON

See https://discuss.prosemirror.net/t/move-node-fromjson-logic-to-schema-nodefromjson/410/5

src/mark.js

@@ -16,14 +16,6 @@ class Mark {
     this.attrs = attrs
   }
 
-  // :: () → Object
-  // Convert this mark to a JSON-serializeable representation.
-  toJSON() {
-    let obj = {_: this.type.name}
-    for (let attr in this.attrs) obj[attr] = this.attrs[attr]
-    return obj
-  }
-
   // :: ([Mark]) → [Mark]
   // Given a set of marks, create a new set which contains this one as
   // well, in the right position. If this mark is already in the set,
@@ -73,6 +65,25 @@ class Mark {
     return true
   }
 
+  // :: () → Object
+  // Convert this mark to a JSON-serializeable representation.
+  toJSON() {
+    let obj = {_: this.type.name}
+    for (let attr in this.attrs) obj[attr] = this.attrs[attr]
+    return obj
+  }
+
+  // :: (Schema, Object) → Mark
+  static fromJSON(schema, json) {
+    let type = schema.marks[json._]
+    let attrs = null
+    for (let prop in json) if (prop != "_") {
+      if (!attrs) attrs = Object.create(null)
+      attrs[prop] = json[prop]
+    }
+    return attrs ? type.create(attrs) : type.instance
+  }
+
   // :: ([Mark], [Mark]) → bool
   // Test whether two sets of marks are identical.
   static sameSet(a, b) {

src/schema.js

@@ -452,13 +452,7 @@ class Schema {
   // Deserialize a mark from its JSON representation. This method is
   // bound.
   markFromJSON(json) {
-    let type = this.marks[json._]
-    let attrs = null
-    for (let prop in json) if (prop != "_") {
-      if (!attrs) attrs = Object.create(null)
-      attrs[prop] = json[prop]
-    }
-    return attrs ? type.create(attrs) : type.instance
+    return Mark.fromJSON(this, json)
   }
 
   // :: (string) → NodeType