Some additional comments, improvement in error handling

src/es5.js

@@ -11,6 +11,8 @@ import {
 } from "./common"
 import {ImmerScope} from "./scope"
 
+// property descriptors are recycled to make sure we don't create a get and set closure per property,
+// but share them all instead
 const descriptors = {}
 
 export function willFinalize(scope, result, isReplaced) {

src/immer.js

@@ -57,13 +57,15 @@ export class Immer {
         if (isDraftable(base)) {
             const scope = ImmerScope.enter()
             const baseDraft = this.createDraft(base)
+            let hasError = true
             try {
                 result = recipe.call(baseDraft, baseDraft)
-            } catch (error) {
-                scope.revoke()
-                throw error
+                hasError = false
+            } finally {
+                // finally instead of catch + rethrow better preserves original stack
+                if (hasError) scope.revoke()
+                else scope.leave()
             }
-            scope.leave()
             if (result instanceof Promise) {
                 return result.then(
                     result => {

src/proxy.js

@@ -40,7 +40,9 @@ export function createDraft(base, parent) {
     }
 
     const {revoke, proxy} = Array.isArray(base)
-        ? Proxy.revocable([state], arrayTraps)
+        ? // [state] is used for arrays, to make sure the proxy is array-ish and not violate invariants,
+          // although state itself is an object
+          Proxy.revocable([state], arrayTraps)
         : Proxy.revocable(state, objectTraps)
 
     state.draft = proxy
@@ -92,6 +94,7 @@ arrayTraps.set = function(state, prop, value) {
     return objectTraps.set.call(this, state[0], prop, value)
 }
 
+// returns the object we should be reading the current value from, which is base, until some change has been made
 function source(state) {
     return state.copy || state.base
 }