fix console instanceof Console (denoland#2073)

js/console.ts

@@ -483,14 +483,18 @@ type PrintFunc = (x: string, isErr?: boolean) => void;
 
 const countMap = new Map<string, number>();
 const timerMap = new Map<string, number>();
+export const isConsoleInstance = Symbol("isConsoleInstance");
 
 export class Console {
   indentLevel: number;
   collapsedAt: number | null;
+  [isConsoleInstance]: boolean = false;
+
   /** @internal */
   constructor(private printFunc: PrintFunc) {
     this.indentLevel = 0;
     this.collapsedAt = null;
+    this[isConsoleInstance] = true;
   }
 
   /** Writes the arguments to stdout */
@@ -730,6 +734,10 @@ export class Console {
     cursorTo(stdout, 0, 0);
     clearScreenDown(stdout);
   };
+
+  static [Symbol.hasInstance](instance: Console): boolean {
+    return instance[isConsoleInstance];
+  }
 }
 
 /**

js/console_test.ts

@@ -20,6 +20,11 @@ test(function consoleShouldBeANamespace() {
   assertEquals(prototype2, Object.prototype);
 });
 
+test(function consoleHasRightInstance() {
+  assert(console instanceof Console);
+  assertEquals({} instanceof Console, false);
+});
+
 test(function consoleTestAssertShouldNotThrowError() {
   console.assert(true);
 

js/globals.ts

@@ -52,6 +52,7 @@ Object.freeze(window.Deno);
 // by ObjectCreate(%ObjectPrototype%), instead of %ObjectPrototype%.
 let console = Object.create({}) as consoleTypes.Console;
 Object.assign(console, new consoleTypes.Console(core.print));
+console[consoleTypes.isConsoleInstance] = true;
 
 // Globally available functions and object instances.
 window.atob = textEncoding.atob;