diff --git a/README.md b/README.md
index aae2b13..ded57fd 100644
--- a/README.md
+++ b/README.md
@@ -316,6 +316,11 @@ jsesc([ 'foo\x00bar', [1, '©', { 'foo': true, 'qux': null }], 42 ], {
   'json': true
 });
 // → '["foo\\u0000bar",[1,"\\u00A9",{"foo":true,"qux":null}],42]'
+// Undefined object properties are skipped, similarily to `JSON.stringify()`:
+jsesc({ foo: undefined, bar: null }, {
+  'json': true
+});
+// → '{"bar": null}'
 // Values that aren’t allowed in JSON are run through `JSON.stringify()`:
 jsesc([ undefined, -Infinity ], {
   'json': true
diff --git a/jsesc.js b/jsesc.js
index 7b8b923..46b25a6 100644
--- a/jsesc.js
+++ b/jsesc.js
@@ -2,9 +2,11 @@
 
 const object = {};
 const hasOwnProperty = object.hasOwnProperty;
-const forOwn = (object, callback) => {
+const forOwn = (object, callback, noUndefined) => {
 	for (const key in object) {
-		if (hasOwnProperty.call(object, key)) {
+		if (hasOwnProperty.call(object, key) &&
+        (!noUndefined || (typeof object[key] !== 'undefined'))
+		) {
 			callback(key, object[key]);
 		}
 	}
@@ -225,7 +227,7 @@ const jsesc = (argument, options) => {
 					(compact ? '' : ' ') +
 					jsesc(value, options)
 				);
-			});
+			}, !!json);
 			if (isEmpty) {
 				return '{}';
 			}
diff --git a/src/jsesc.js b/src/jsesc.js
index d3eaff1..fe677b4 100644
--- a/src/jsesc.js
+++ b/src/jsesc.js
@@ -2,9 +2,11 @@
 
 const object = {};
 const hasOwnProperty = object.hasOwnProperty;
-const forOwn = (object, callback) => {
+const forOwn = (object, callback, noUndefined) => {
 	for (const key in object) {
-		if (hasOwnProperty.call(object, key)) {
+		if (hasOwnProperty.call(object, key) &&
+        (!noUndefined || (typeof object[key] !== 'undefined'))
+		) {
 			callback(key, object[key]);
 		}
 	}
@@ -225,7 +227,7 @@ const jsesc = (argument, options) => {
 					(compact ? '' : ' ') +
 					jsesc(value, options)
 				);
-			});
+			}, !!json);
 			if (isEmpty) {
 				return '{}';
 			}