Implement diffAsString function

README.md

@@ -29,6 +29,27 @@ uninspected.diff({ foo: 'bar' }, { foo: 'baz' });
 }
 ```
 
+Or if you want to get the rendered diff as a string:
+
+```javascript
+const diff = uninspected.diffAsString({ foo: 'bar' }, { foo: 'baz' });
+```
+
+You can also ask for the diff with ANSI codes, or in HTML format:
+
+```javascript
+const ansiDiff = uninspected.diffAsString(
+  { foo: 'bar' },
+  { foo: 'baz' },
+  'ansi'
+);
+const htmlDiff = uninspected.diffAsString(
+  { foo: 'bar' },
+  { foo: 'baz' },
+  'html'
+);
+```
+
 You can also use it instead of the console object:
 
 ```javascript

lib/uninspected.js

@@ -23,7 +23,7 @@ uninspected.inspect = (obj, options) => {
 
 uninspected.defaultDepth = 6; // util's default level of 2 is annoyingly low
 uninspected.output = unexpected.output;
-uninspected.createOutput = unexpected.createOutput;
+uninspected.createOutput = unexpected.createOutput.bind(unexpected);
 uninspected.outputFormat = unexpected.outputFormat();
 
 if (uninspected.outputFormat === 'html') {
@@ -36,9 +36,9 @@ const isChrome =
   typeof navigator.userAgent === 'string' &&
   /chrome/i.test(navigator.userAgent);
 
-function createOutput() {
+function createOutput(format) {
   return uninspected.createOutput(
-    isChrome ? 'coloredConsole' : uninspected.outputFormat
+    format || (isChrome ? 'coloredConsole' : uninspected.outputFormat)
   );
 }
 
@@ -71,23 +71,27 @@ uninspected.assert = (subject) => {
   unexpected(subject, 'to be truthy');
 };
 
-uninspected.diff = (a, b) => {
-  const result = unexpected.diff(a, b, createOutput());
+function renderDiff(a, b, format) {
+  const result = unexpected.diff(a, b, createOutput(format));
   if (result) {
-    uninspected.log(result);
+    return createOutput(format).append(result);
   } else if (unexpected.equal(a, b)) {
-    uninspected.log(a);
+    return createOutput(format).appendInspected(a);
   } else {
-    uninspected.log(
-      unexpected.output
-        .clone()
-        .text('-')
-        .append(unexpected.inspect(a))
-        .nl()
-        .text('+')
-        .append(unexpected.inspect(b))
-    );
+    return createOutput(format)
+      .text('-')
+      .append(unexpected.inspect(a))
+      .nl()
+      .text('+')
+      .append(unexpected.inspect(b));
   }
+}
+
+uninspected.diffAsString = (a, b, format) =>
+  renderDiff(a, b, format || 'text').toString();
+
+uninspected.diff = (a, b) => {
+  uninspected.log(renderDiff(a, b));
 };
 
 // Support trace, time, timeEnd etc.

test/uninspected.js

@@ -71,6 +71,47 @@ describe('uninspected', () => {
     });
   });
 
+  describe('#diffAsString', () => {
+    it('should render a diff in text format by default', () => {
+      expect(
+        uninspected.diffAsString({ foo: 'bar' }, { foo: 'baz' }),
+        'to equal',
+        '{\n' +
+          "  foo: 'bar' // should equal 'baz'\n" +
+          '             //\n' +
+          '             // -bar\n' +
+          '             // +baz\n' +
+          '}'
+      );
+    });
+
+    it('should render a diff in ansi format if requested', () => {
+      expect(
+        uninspected.diffAsString({ foo: 'bar' }, { foo: 'baz' }, 'ansi'),
+        'to equal',
+        '{\n' +
+          "  \x1b[90m\x1b[38;5;242mfoo\x1b[39m: \x1b[36m'bar'\x1b[39m \x1b[31m\x1b[1m//\x1b[22m\x1b[39m \x1b[31m\x1b[1mshould equal\x1b[22m\x1b[39m \x1b[36m'baz'\x1b[39m\n" +
+          '             \x1b[31m\x1b[1m//\x1b[22m\x1b[39m\n' +
+          '             \x1b[31m\x1b[1m//\x1b[22m\x1b[39m \x1b[41m\x1b[30mbar\x1b[39m\x1b[49m\n' +
+          '             \x1b[31m\x1b[1m//\x1b[22m\x1b[39m \x1b[42m\x1b[30mbaz\x1b[39m\x1b[49m\n' +
+          '}'
+      );
+    });
+
+    it('should render the actual value if there is no diff', () => {
+      expect(
+        uninspected.diffAsString({ foo: 'bar' }, { foo: 'bar' }),
+        'to equal',
+        "{\n  foo: 'bar'\n}"
+      );
+    });
+
+    it('should do something reasonable when diffing primitive values with no specific built-in diff', () => {
+      uninspected.outputFormat = 'text';
+      expect(uninspected.diffAsString(123, 456), 'to equal', '-123\n+456');
+    });
+  });
+
   describe('#diff', () => {
     beforeEach(() => {
       sinon.stub(console, 'log');