Refactoring assoc/assocIn for updating field state

Author: davidkpiano

src/utils/create-field.js

@@ -24,6 +24,15 @@ function getSubModelString(model, subModel) {
   return `${model}.${subModel}`;
 }
 
+export function updateFieldState(existingFieldState, updatedFieldState) {
+  const newField = {
+    ...existingFieldState,
+    ...updatedFieldState,
+  };
+
+  return newField;
+}
+
 export default function createFieldState(model, value, customInitialFieldState) {
   return {
     ...initialFieldState,

src/utils/update-field.js

@@ -2,19 +2,42 @@ import i from 'icepick';
 import get from './get';
 import mapValues from './map-values';
 import { createInitialState } from '../reducers/form-reducer';
+import { updateFieldState } from './create-field';
+import identity from './identity';
 import invariant from 'invariant';
 
-function assocIn(state, path, value, fn) {
-  if (!path.length) return i.assign(state, value);
-  if (!fn) return i.assocIn(state, path, value);
+function objClone(obj) {
+  const keys = Object.keys(obj);
+  const length = keys.length;
+  const result = {};
+  let index = 0;
+  let key;
+
+  for (; index < length; index += 1) {
+    key = keys[index];
+    result[key] = obj[key];
+  }
+  return result;
+}
+
+function assoc(state, key, value) {
+  const newState = objClone(state);
+
+  newState[key] = value;
+
+  return newState;
+}
+
+function assocIn(state, path, value, fn = identity) {
+  if (!path.length) return value;
 
   const key0 = path[0];
 
   if (path.length === 1) {
-    return fn(i.assoc(state, key0, value));
+    return fn(assoc(state, key0, value));
   }
 
-  return fn(i.assoc(state, key0, assocIn(state[key0] || {}, path.slice(1), value, fn)));
+  return fn(assoc(state, key0, assocIn(state[key0] || {}, path.slice(1), value, fn)));
 }
 
 function tempInitialState(path, initialValue = null) {
@@ -53,7 +76,7 @@ export default function updateField(state, path, newState, newSubState, updater)
 
   const isForm = field.hasOwnProperty('$form');
   const fieldPath = isForm
-    ? i.push(path, '$form')
+    ? [...path, '$form']
     : path;
 
   const fieldState = isForm
@@ -67,24 +90,22 @@ export default function updateField(state, path, newState, newSubState, updater)
   if (isForm && newSubState) {
     const formState = mapValues(field, (subState, key) => {
       if (key === '$form') {
-        return i.assign(
-          fieldState,
-          updatedFieldState);
+        return updateFieldState(fieldState, updatedFieldState);
       }
 
       const updatedSubState = typeof newSubState === 'function'
         ? newSubState(subState, updatedFieldState)
         : newSubState;
 
-      return i.assign(subState, updatedSubState);
+      return updateFieldState(subState, updatedSubState);
     });
 
     if (!path.length) return formState;
 
     return assocIn(fullState, path, formState, updater);
   }
 
-  return assocIn(fullState, fieldPath, i.assign(
+  return assocIn(fullState, fieldPath, updateFieldState(
     fieldState,
     updatedFieldState), updater);
 }