Error pretty print (print stack)

js/console.ts

@@ -6,54 +6,41 @@ function getClassInstanceName(instance: any): string {
   if (typeof instance !== "object") {
     return "";
   }
-  if (instance && instance.__proto__ && instance.__proto__.constructor) {
-    return instance.__proto__.constructor.name; // could be "Object" or "Array"
+  if (instance) {
+    const proto = Object.getPrototypeOf(instance);
+    if (proto && proto.constructor) {
+      return proto.constructor.name; // could be "Object" or "Array"
+    }
   }
   return "";
 }
 
-// tslint:disable-next-line:no-any
-function stringify(ctx: ConsoleContext, value: any): string {
-  switch (typeof value) {
-    case "string":
-      return value;
-    case "number":
-    case "boolean":
-    case "undefined":
-    case "symbol":
-      return String(value);
-    case "function":
+function createFunctionString(value: Function, ctx: ConsoleContext): string {
   // Might be Function/AsyncFunction/GeneratorFunction
-      const cstrName = value.__proto__.constructor.name;
+  const cstrName = Object.getPrototypeOf(value).constructor.name;
   if (value.name && value.name !== "anonymous") {
     // from MDN spec
     return `[${cstrName}: ${value.name}]`;
   }
   return `[${cstrName}]`;
-    case "object":
-      if (value === null) {
-        return "null";
 }
 
-      if (ctx.has(value)) {
-        return "[Circular]";
-      }
-
-      ctx.add(value);
+// tslint:disable-next-line:no-any
+function createArrayString(value: any[], ctx: ConsoleContext): string {
   const entries: string[] = [];
-
-      if (Array.isArray(value)) {
   for (const el of value) {
     entries.push(stringifyWithQuotes(ctx, el));
   }
-
   ctx.delete(value);
-
   if (entries.length === 0) {
     return "[]";
   }
   return `[ ${entries.join(", ")} ]`;
-      } else {
+}
+
+// tslint:disable-next-line:no-any
+function createObjectString(value: any, ctx: ConsoleContext): string {
+  const entries: string[] = [];
   let baseString = "";
 
   const className = getClassInstanceName(value);
@@ -80,6 +67,37 @@ function stringify(ctx: ConsoleContext, value: any): string {
 
   return baseString;
 }
+
+// tslint:disable-next-line:no-any
+function stringify(ctx: ConsoleContext, value: any): string {
+  switch (typeof value) {
+    case "string":
+      return value;
+    case "number":
+    case "boolean":
+    case "undefined":
+    case "symbol":
+      return String(value);
+    case "function":
+      return createFunctionString(value as Function, ctx);
+    case "object":
+      if (value === null) {
+        return "null";
+      }
+
+      if (ctx.has(value)) {
+        return "[Circular]";
+      }
+      ctx.add(value);
+
+      if (value instanceof Error) {
+        return value.stack! || "";
+      } else if (Array.isArray(value)) {
+        // tslint:disable-next-line:no-any
+        return createArrayString(value as any[], ctx);
+      } else {
+        return createObjectString(value, ctx);
+      }
     default:
       return "[Not Implemented]";
   }

js/console_test.ts

@@ -91,3 +91,17 @@ test(function consoleTestStringifyCircular() {
     "Console { printFunc: [Function], debug: [Function: log], info: [Function: log], error: [Function: warn] }"
   );
 });
+
+test(function consoleTestError() {
+  class MyError extends Error {
+    constructor(msg: string) {
+      super(msg);
+      this.name = "MyError";
+    }
+  }
+  try {
+    throw new MyError("This is an error");
+  } catch (e) {
+    assertEqual(stringify(e).split("\n")[0], "MyError: This is an error");
+  }
+});