fix undefined values

closes #44

lib/prettyjson.js

@@ -13,6 +13,7 @@ var isSerializable = function(input, onlyPrimitives, options) {
     typeof input === 'number' ||
     typeof input === 'function' ||
     input === null ||
+    input === undefined ||
     input instanceof Date
   ) {
     return true;
@@ -48,7 +49,7 @@ var addColorToData = function(input, options) {
   if (input === false) {
     return colors.red(sInput);
   }
-  if (input === null) {
+  if (input === null || input === undefined) {
     return colors.grey(sInput);
   }
   if (typeof input === 'number') {
@@ -158,11 +159,6 @@ var renderToArray = function(data, options, indentation) {
     }
     key = Utils.indent(indentation) + key;
 
-    // Skip `undefined`, it's not a valid JSON value.
-    if (data[i] === undefined) {
-      return;
-    }
-
     // If the value is serializable, render it in the same line
     if (isSerializable(data[i], false, options)) {
       var nextIndentation = options.noAlign ? 0 : maxIndexLength - i.length;

test/prettyjson_spec.js

@@ -292,6 +292,29 @@ describe('Printing numbers, booleans and other objects', function() {
     output.should.equal('    ' + colors.grey('null'));
   });
 
+  it('should print a undefined object correctly ', function() {
+    var input;
+    var output = prettyjson.render(input, {}, 4);
+
+    output.should.equal('    ' + colors.grey('undefined'));
+  });
+
+  it('should print undefined keys ', function() {
+    var input = {
+      foo: undefined,
+      bar: [1, undefined, 2],
+    };
+    var output = prettyjson.render(input, {}, 4);
+
+    output.should.equal(([
+      '    ' + colors.green('foo: ') + colors.grey('undefined'),
+      '    ' + colors.green('bar: '),
+      '      ' + colors.green('- ') + colors.blue(1),
+      '      ' + colors.green('- ') + colors.grey('undefined'),
+      '      ' + colors.green('- ') + colors.blue(2)
+    ].join('\n')));
+  });
+
   it('should print an Error correctly ', function() {
     Error.stackTraceLimit = 1;
     var input = new Error('foo');