fix: out of range assignments were broken in ES5 mode. Fixes #638

__tests__/regressions.js

@@ -89,7 +89,7 @@ function runBaseTest(name, useProxies, autoFreeze, useListener) {
 			expect(foo2).toBe(foo)
 		})
 
-		test("#646 -2 setting undefined field to undefined should not create new result", () => {
+		test("#646 - 2 setting undefined field to undefined should not create new result", () => {
 			const foo = {}
 			const foo2 = produce(foo, draft => {
 				draft.bar = undefined
@@ -98,5 +98,23 @@ function runBaseTest(name, useProxies, autoFreeze, useListener) {
 			expect(foo).toEqual({})
 			expect(foo2).toEqual({bar: undefined})
 		})
+
+		test("#638 - out of range assignments", () => {
+			const state = []
+
+			const state1 = produce(state, draft => {
+				draft[2] = "v2"
+			})
+
+			expect(state1.length).toBe(3)
+			expect(state1).toEqual([undefined, undefined, "v2"])
+
+			const state2 = produce(state1, draft => {
+				draft[1] = "v1"
+			})
+
+			expect(state2.length).toBe(3)
+			expect(state2).toEqual([undefined, "v1", "v2"])
+		})
 	})
 }

src/plugins/es5.ts

@@ -46,24 +46,22 @@ export function enableES5() {
 	}
 
 	function createES5Draft(isArray: boolean, base: any) {
-		// Create a new object / array, where each own property is trapped with an accessor
-		const descriptors = getOwnPropertyDescriptors(base)
-		// Descriptors we want to skip:
-		if (isArray) delete descriptors.length
-		delete descriptors[DRAFT_STATE as any]
-		const keys = ownKeys(descriptors)
-		for (let i = 0; i < keys.length; i++) {
-			const key: any = keys[i]
-			descriptors[key] = proxyProperty(
-				key,
-				isArray || !!descriptors[key].enumerable
-			)
-		}
 		if (isArray) {
 			const draft = new Array(base.length)
-			Object.defineProperties(draft, descriptors)
+			for (let i = 0; i < base.length; i++)
+				Object.defineProperty(draft, "" + i, proxyProperty(i, true))
 			return draft
 		} else {
+			const descriptors = getOwnPropertyDescriptors(base)
+			delete descriptors[DRAFT_STATE as any]
+			const keys = ownKeys(descriptors)
+			for (let i = 0; i < keys.length; i++) {
+				const key: any = keys[i]
+				descriptors[key] = proxyProperty(
+					key,
+					isArray || !!descriptors[key].enumerable
+				)
+			}
 			return Object.create(Object.getPrototypeOf(base), descriptors)
 		}
 	}