console, internal/jsre: colorize JavaScript exceptions too

2 files changed, 20 insertions, 2 deletions

diff --git a/internal/jsre/jsre.go b/internal/jsre/jsre.go
index 8d8f4fc2a..a95efd379 100644
--- a/internal/jsre/jsre.go
+++ b/internal/jsre/jsre.go
@@ -303,11 +303,11 @@ func (self *JSRE) Evaluate(code string, w io.Writer) error {
 	self.Do(func(vm *otto.Otto) {
 		val, err := vm.Run(code)
 		if err != nil {
-			fail = err
+			prettyError(vm, err, w)
 		} else {
 			prettyPrint(vm, val, w)
-			fmt.Fprintln(w)
 		}
+		fmt.Fprintln(w)
 	})
 	return fail
 }
diff --git a/internal/jsre/pretty.go b/internal/jsre/pretty.go
index cf4bf2cf8..30d8660ff 100644
--- a/internal/jsre/pretty.go
+++ b/internal/jsre/pretty.go
@@ -37,6 +37,7 @@ var (
 	SpecialColor  = color.New(color.Bold).SprintfFunc()
 	NumberColor   = color.New(color.FgRed).SprintfFunc()
 	StringColor   = color.New(color.FgGreen).SprintfFunc()
+	ErrorColor    = color.New(color.FgHiRed).SprintfFunc()
 )
 
 // these fields are hidden when printing objects.
@@ -55,6 +56,23 @@ func prettyPrint(vm *otto.Otto, value otto.Value, w io.Writer) {
 	ppctx{vm: vm, w: w}.printValue(value, 0, false)
 }
 
+// prettyError writes err to standard output.
+func prettyError(vm *otto.Otto, err error, w io.Writer) {
+	failure := err.Error()
+	if ottoErr, ok := err.(*otto.Error); ok {
+		failure = ottoErr.String()
+	}
+	fmt.Fprint(w, ErrorColor("%s", failure))
+}
+
+// jsErrorString adds a backtrace to errors generated by otto.
+func jsErrorString(err error) string {
+	if ottoErr, ok := err.(*otto.Error); ok {
+		return ottoErr.String()
+	}
+	return err.Error()
+}
+
 func prettyPrintJS(call otto.FunctionCall, w io.Writer) otto.Value {
 	for _, v := range call.ArgumentList {
 		prettyPrint(call.Otto, v, w)