feat(ui): add ability to output to stderr

closes #218
- add stderr option to log method
- change error method to output most things to stderr rather than stdout

lib/ui/index.js

@@ -122,12 +122,14 @@ class UI {
         });
     }
 
-    log(message, color) {
+    log(message, color, stderr) {
         if (color) {
             message = chalk[color](message);
         }
 
-        this.stdout.write(`${this.spinner ? '\r' : ''}${message}\n`);
+        let stream = stderr ? 'stderr' : 'stdout';
+
+        this[stream].write(`${this.spinner ? '\r' : ''}${message}\n`);
     }
 
     success(message) {
@@ -157,7 +159,7 @@ class UI {
             let verboseOutput = error.toString(true);
 
             // Log the verbose error if verbose is set, otherwise log the non-verbose error output
-            this.log(this.verbose ? verboseOutput : error.toString(false));
+            this.log(this.verbose ? verboseOutput : error.toString(false), null, true);
             this.log(debugInfo, 'yellow');
 
             if (error.logToFile()) {
@@ -168,7 +170,7 @@ class UI {
             let output = `An error occurred.\n${chalk.yellow('Message:')} '${error.message}'\n\n`;
 
             if (!this.verbose) {
-                this.log(output, 'red');
+                this.log(output, 'red', true);
             }
 
             if (error.stack) {
@@ -184,17 +186,17 @@ class UI {
             }
 
             if (this.verbose) {
-                this.log(output, 'red');
+                this.log(output, 'red', true);
             }
 
             this.log(debugInfo, 'yellow');
             this._logErrorToFile(`${debugInfo}\n${output}`);
         } else if (isObject(error)) {
             // TODO: find better way to handle object errors?
-            this.log(JSON.stringify(error));
+            this.log(JSON.stringify(error), null, true);
         } else if (error !== false) {
             // If the error is false, we're just exiting (makes the promise chains easier)
-            this.log('An unknown error occured.');
+            this.log('An unknown error occured.', null, true);
         }
     }