feat(undefined): printing undefined property values, closes #20

README.md

@@ -114,14 +114,14 @@ arguments - there is no performance penalty!
 ## Rethrowing errors
 
 If the condition itself is an instance of Error, it is simply rethrown (synchronously or
-asynchronously). 
+asynchronously).
 
 ```js
 lazyAss(new Error('foo'));
 // Uncaught Error: foo
 ```
 
-Useful to make sure errors in the promise chains are 
+Useful to make sure errors in the promise chains are
 [not silently ignored](https://glebbahmutov.com/blog/why-promises-need-to-be-done/).
 
 For example, a rejected promise below this will be ignored.
@@ -241,19 +241,19 @@ WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 OTHER DEALINGS IN THE SOFTWARE.
 
-[lazy-ass-icon]: https://nodei.co/npm/lazy-ass.png?downloads=true
+[lazy-ass-icon]: https://nodei.co/npm/lazy-ass.svg?downloads=true
 [lazy-ass-url]: https://npmjs.org/package/lazy-ass
-[lazy-ass-ci-image]: https://travis-ci.org/bahmutov/lazy-ass.png?branch=master
+[lazy-ass-ci-image]: https://travis-ci.org/bahmutov/lazy-ass.svg?branch=master
 [lazy-ass-ci-url]: https://travis-ci.org/bahmutov/lazy-ass
-[lazy-ass-coverage-image]: https://coveralls.io/repos/bahmutov/lazy-ass/badge.png
+[lazy-ass-coverage-image]: https://coveralls.io/repos/bahmutov/lazy-ass/badge.svg
 [lazy-ass-coverage-url]: https://coveralls.io/r/bahmutov/lazy-ass
 [lazy-ass-code-climate-image]: https://codeclimate.com/github/bahmutov/lazy-ass/badges/gpa.svg
 [lazy-ass-code-climate-url]: https://codeclimate.com/github/bahmutov/lazy-ass
 [lazy-ass-codacy-image]: https://www.codacy.com/project/badge/b60a0810c9af4fe4b2ae685932dbbdb8
 [lazy-ass-codacy-url]: https://www.codacy.com/public/bahmutov/lazy-ass.git
-[lazy-ass-dependencies-image]: https://david-dm.org/bahmutov/lazy-ass.png
+[lazy-ass-dependencies-image]: https://david-dm.org/bahmutov/lazy-ass.svg
 [lazy-ass-dependencies-url]: https://david-dm.org/bahmutov/lazy-ass
-[lazy-ass-devdependencies-image]: https://david-dm.org/bahmutov/lazy-ass/dev-status.png
+[lazy-ass-devdependencies-image]: https://david-dm.org/bahmutov/lazy-ass/dev-status.svg
 [lazy-ass-devdependencies-url]: https://david-dm.org/bahmutov/lazy-ass#info=devDependencies
 [semantic-image]: https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg
 [semantic-url]: https://github.com/semantic-release/semantic-release

index.html

@@ -41,7 +41,11 @@ <h1>lazy-ass</h1>
       bar.bar = bar;
       lac(false, 'example printing a circular object', bar);
 
-      la(typeof foo === 'string', 'sync exception, variable foo is a string', foo);
+      lac(false, {foo: 'foo', bar: undefined},
+        'this object has property "bar" with undefined value')
+
+      la(typeof foo === 'string',
+        'sync exception, variable foo is NOT a string, but', typeof foo, foo);
       // nothing runs after sync exception
     </script>
   </body>

index.js

@@ -19,6 +19,23 @@
     return e instanceof Error;
   }
 
+  /*
+    custom JSON.stringify replacer to make sure we do not
+    hide properties that have value "undefined"
+    var o = {
+      foo: 42,
+      bar: undefined
+    }
+    // standard JSON.stringify returns '{"foo": 42}'
+    // this replacer returns '{"foo": 42, "bar": null}'
+  */
+  function replacer(key, value) {
+    if (value === undefined) {
+      return null;
+    }
+    return value;
+  }
+
   function toString(arg, k) {
     if (isPrimitive(arg)) {
       return JSON.stringify(arg);
@@ -35,7 +52,7 @@
     }
     var argString;
     try {
-      argString = JSON.stringify(arg, null, 2);
+      argString = JSON.stringify(arg, replacer, 2);
     } catch (err) {
       argString = '{ cannot stringify arg ' + k + ', it has type "' + typeof arg + '"';
       if (typeof arg === 'object') {

test/lazy-ass.spec.js

@@ -140,6 +140,64 @@
         }).to.throwException(JSON.stringify(obj, null, 2));
       });
 
+      it('JSON.stringify skip undefined property', function () {
+        var obj = {
+          foo: 'foo',
+          bad: undefined
+        };
+        const str = JSON.stringify(obj);
+        expect(str).not.to.contain('bad', str);
+      });
+
+      it('JSON.stringify with custom replacer', function () {
+        var obj = {
+          foo: 'foo',
+          bad: undefined
+        };
+        function replacer(key, value) {
+          if (value === undefined) {
+            return 'null';
+          }
+          return value;
+        }
+        const str = JSON.stringify(obj, replacer);
+        expect(str).to.contain('foo', str);
+        expect(str).to.contain('bad', str);
+      });
+
+      it('nested JSON.stringify with custom replacer', function () {
+        var obj = {
+          foo: 'foo',
+          bar: {
+            baz: 'value'
+          }
+        };
+        function replacer(key, value) {
+          if (value === undefined) {
+            return null;
+          }
+          return value;
+        }
+        const str = JSON.stringify(obj, replacer);
+        expect(str).to.contain('foo', str);
+        expect(str).to.contain('bar', str);
+        expect(str).to.contain('baz', str);
+        expect(str).to.contain('value', str);
+      });
+
+      it('JSON stringifies undefined value of a property', function () {
+        var obj = {
+          foo: 'foo',
+          bad: undefined
+        };
+        expect(function () {
+          lazyAss(false, obj);
+        }).to.throwException(function (err) {
+          expect(err.message).to.contain('foo', err.message);
+          expect(err.message).to.contain('bad', err.message);
+        });
+      });
+
       it('takes error name and message', function () {
         expect(function () {
           lazyAss(false, new Error('hi there'));