Skip undefined properties for options.json = true;

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

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 '{}';
 			}

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 '{}';
 			}

tests/tests.js

@@ -605,7 +605,7 @@ describe('advanced tests', function() {
 
 		// Some of these depend on `JSON.parse()`, so only test them in Node
 		const testArray = [
-			undefined, Infinity, new Number(Infinity), -Infinity,
+			undefined, { foo: undefined }, Infinity, new Number(Infinity), -Infinity,
 			new Number(-Infinity), 0, new Number(0), -0, new Number(-0), +0,
 			new Number(+0), new Function(), 'str',
 			function zomg() { return 'desu'; }, null, true, new Boolean(true),
@@ -617,23 +617,23 @@ describe('advanced tests', function() {
 			jsesc(testArray, {
 				'json': false
 			}),
-			'[undefined,Infinity,Infinity,-Infinity,-Infinity,0,0,0,0,0,0,function anonymous() {\n\n},\'str\',function zomg() { return \'desu\'; },null,true,true,false,false,{\'foo\':42,\'hah\':[1,2,3,{\'foo\':42}]}]',
+			'[undefined,{\'foo\':undefined},Infinity,Infinity,-Infinity,-Infinity,0,0,0,0,0,0,function anonymous() {\n\n},\'str\',function zomg() { return \'desu\'; },null,true,true,false,false,{\'foo\':42,\'hah\':[1,2,3,{\'foo\':42}]}]',
 			'Escaping a non-flat array with all kinds of values'
 		);
 		assert.equal(
 			jsesc(testArray, {
 				'json': true
 			}),
-			'[null,null,null,null,null,0,0,0,0,0,0,null,"str",null,null,true,true,false,false,{"foo":42,"hah":[1,2,3,{"foo":42}]}]',
+			'[null,{},null,null,null,null,0,0,0,0,0,0,null,"str",null,null,true,true,false,false,{"foo":42,"hah":[1,2,3,{"foo":42}]}]',
 			'Escaping a non-flat array with all kinds of values, with `json: true`'
 		);
 		assert.equal(
 			jsesc(testArray, {
 				'json': true,
 				'compact': false
 			}),
-			'[\n\tnull,\n\tnull,\n\tnull,\n\tnull,\n\tnull,\n\t0,\n\t0,\n\t0,\n\t0,\n\t0,\n\t0,\n\tnull,\n\t"str",\n\tnull,\n\tnull,\n\ttrue,\n\ttrue,\n\tfalse,\n\tfalse,\n\t{\n\t\t"foo": 42,\n\t\t"hah": [\n\t\t\t1,\n\t\t\t2,\n\t\t\t3,\n\t\t\t{\n\t\t\t\t"foo": 42\n\t\t\t}\n\t\t]\n\t}\n]',
+			'[\n\tnull,\n\t{},\n\tnull,\n\tnull,\n\tnull,\n\tnull,\n\t0,\n\t0,\n\t0,\n\t0,\n\t0,\n\t0,\n\tnull,\n\t"str",\n\tnull,\n\tnull,\n\ttrue,\n\ttrue,\n\tfalse,\n\tfalse,\n\t{\n\t\t"foo": 42,\n\t\t"hah": [\n\t\t\t1,\n\t\t\t2,\n\t\t\t3,\n\t\t\t{\n\t\t\t\t"foo": 42\n\t\t\t}\n\t\t]\n\t}\n]',
 			'Escaping a non-flat array with all kinds of values, with `json: true, compact: false`'
 		);
-	}).timeout(25000);
+	}).timeout(30000);
 });