From 7fba690f5293dd2fe0e6095b5f184d60d697cae3 Mon Sep 17 00:00:00 2001
From: Brian Donovan <me@brian-donovan.com>
Date: Mon, 21 Dec 2015 15:26:27 -0800
Subject: [PATCH] Ensure `delete` operations at the top level are preserved.

Fixes #352.
---
 src/Statement.js                |  4 ++--
 src/ast/modifierNodes.js        | 19 +++++++++++++++++--
 src/utils/run.js                |  4 ++--
 test/function/delete/_config.js |  3 +++
 test/function/delete/main.js    |  4 ++++
 5 files changed, 28 insertions(+), 6 deletions(-)
 create mode 100644 test/function/delete/_config.js
 create mode 100644 test/function/delete/main.js

diff --git a/src/Statement.js b/src/Statement.js
index a9efc49..4852167 100644
--- a/src/Statement.js
+++ b/src/Statement.js
@@ -1,7 +1,7 @@
 import { walk } from 'estree-walker';
 import Scope from './ast/Scope.js';
 import attachScopes from './ast/attachScopes.js';
-import modifierNodes from './ast/modifierNodes.js';
+import modifierNodes, { isModifierNode } from './ast/modifierNodes.js';
 import isFunctionDeclaration from './ast/isFunctionDeclaration.js';
 import isReference from './ast/isReference.js';
 import getLocation from './utils/getLocation.js';
@@ -95,7 +95,7 @@ export default class Statement {
 
 				let isReassignment;
 
-				if ( parent && parent.type in modifierNodes ) {
+				if ( parent && isModifierNode( parent ) ) {
 					let subject = parent[ modifierNodes[ parent.type ] ];
 					let depth = 0;
 
diff --git a/src/ast/modifierNodes.js b/src/ast/modifierNodes.js
index 2ea3f5d..3696fd1 100644
--- a/src/ast/modifierNodes.js
+++ b/src/ast/modifierNodes.js
@@ -1,4 +1,19 @@
-export default {
+const modifierNodes = {
 	AssignmentExpression: 'left',
-	UpdateExpression: 'argument'
+	UpdateExpression: 'argument',
+	UnaryExpression: 'argument'
 };
+
+export default modifierNodes;
+
+export function isModifierNode ( node ) {
+	if ( !( node.type in modifierNodes ) ) {
+		return false;
+	}
+
+	if ( node.type === 'UnaryExpression' ) {
+		return node.operator === 'delete';
+	}
+
+	return true;
+}
diff --git a/src/utils/run.js b/src/utils/run.js
index ac303f1..aa9306a 100644
--- a/src/utils/run.js
+++ b/src/utils/run.js
@@ -1,5 +1,5 @@
 import { walk } from 'estree-walker';
-import modifierNodes from '../ast/modifierNodes.js';
+import modifierNodes, { isModifierNode } from '../ast/modifierNodes.js';
 import isReference from '../ast/isReference.js';
 import flatten from '../ast/flatten';
 
@@ -115,7 +115,7 @@ export default function run ( node, scope, statement, strongDependencies, force
 				}
 			}
 
-			else if ( node.type in modifierNodes ) {
+			else if ( isModifierNode( node ) ) {
 				let subject = node[ modifierNodes[ node.type ] ];
 				while ( subject.type === 'MemberExpression' ) subject = subject.object;
 
diff --git a/test/function/delete/_config.js b/test/function/delete/_config.js
new file mode 100644
index 0000000..4a5902c
--- /dev/null
+++ b/test/function/delete/_config.js
@@ -0,0 +1,3 @@
+module.exports = {
+  description: '`delete` operator at the top level is preserved'
+};
diff --git a/test/function/delete/main.js b/test/function/delete/main.js
new file mode 100644
index 0000000..ff7a468
--- /dev/null
+++ b/test/function/delete/main.js
@@ -0,0 +1,4 @@
+var a = { b: 1 };
+assert.strictEqual(a.b, 1);
+delete a.b;
+assert.strictEqual(a.b, undefined);