DzmitryShylovich · Feb 5, 2017
diff --git a/modules/@angular/core/src/application_module.ts b/modules/@angular/core/src/application_module.ts
@@ -8,13 +8,14 @@
 
 import {AnimationQueue} from './animation/animation_queue';
 import {APP_INITIALIZER, ApplicationInitStatus} from './application_init';
-import {ApplicationRef, ApplicationRef_} from './application_ref';
+import {ApplicationRef, ApplicationRef_, isDevMode} from './application_ref';
 import {APP_ID_RANDOM_PROVIDER} from './application_tokens';
 import {IterableDiffers, KeyValueDiffers, defaultIterableDiffers, defaultKeyValueDiffers} from './change_detection/change_detection';
 import {Inject, Optional, SkipSelf} from './di/metadata';
 import {LOCALE_ID} from './i18n/tokens';
 import {Compiler} from './linker/compiler';
 import {ViewUtils} from './linker/view_utils';
+import {ConsoleLogger, LOGGER_OPTIONS, Logger, LoggerOptions, NoOpLogger} from './logger';
 import {NgModule} from './metadata';
 import {initServicesIfNeeded} from './view/index';
 
@@ -34,6 +35,17 @@ export function _initViewEngine() {
   initServicesIfNeeded();
 }
 
+export function _loggerFactory(options?: LoggerOptions): Logger {
+  options = options || {};
+  const enabled = options.enabled != null ? options.enabled : isDevMode();
+  if (enabled) {
+    const _console: Console = typeof console === 'object' ? console : <any>{};
+    const debug = options.debug != null ? options.debug : true;
+    return new ConsoleLogger(_console, debug);
+  }
+  return new NoOpLogger();
+}
+
 /**
  * This module includes the providers of @angular/core that are needed
  * to bootstrap components via `ApplicationRef`.
@@ -51,6 +63,11 @@ export function _initViewEngine() {
     AnimationQueue,
     {provide: IterableDiffers, useFactory: _iterableDiffersFactory},
     {provide: KeyValueDiffers, useFactory: _keyValueDiffersFactory},
+    {
+      provide: Logger,
+      useFactory: _loggerFactory,
+      deps: [[new Inject(LOGGER_OPTIONS), new Optional()]]
+    },
     {
       provide: LOCALE_ID,
       useFactory: _localeFactory,

diff --git a/modules/@angular/core/src/core.ts b/modules/@angular/core/src/core.ts
@@ -39,4 +39,5 @@ export {AnimationStyles} from './animation/animation_styles';
 export {AnimationKeyframe} from './animation/animation_keyframe';
 export {Sanitizer, SecurityContext} from './security';
 export {TransitionFactory, TransitionInstruction, Trigger} from './triggers';
+export {Logger, LOGGER_OPTIONS, LoggerOptions} from './logger';
 export * from './codegen_private_exports';
diff --git a/modules/@angular/core/src/logger.ts b/modules/@angular/core/src/logger.ts
@@ -0,0 +1,111 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {InjectionToken} from './di/injection_token';
+
+/** @experimental */
+export interface LoggerOptions {
+  enabled?: boolean;
+  debug?: boolean;
+}
+
+/**
+ * @whatItDoes Is used in DI to configure the {@link Logger}.
+ * @experimental
+ */
+export const LOGGER_OPTIONS = new InjectionToken<LoggerOptions>('Logger Options');
+
+/**
+ * Simple service for logging.
+ *
+ * @experimental
+ */
+export abstract class Logger {
+  /** Write a log message. */
+  abstract log(...args: any[]): void;
+
+  /** Write an information message. */
+  abstract info(...args: any[]): void;
+
+  /** Write a warning message. */
+  abstract warn(...args: any[]): void;
+
+  /** Write an error message. */
+  abstract error(...args: any[]): void;
+
+  /** Write a debug message. */
+  abstract debug(...args: any[]): void;
+
+  /** Create a new inline group. */
+  abstract group(groupTitle?: string): void;
+
+  /** Exit the current inline group. */
+  abstract groupEnd(): void;
+}
+
+const noop = (): any => undefined;
+
+/**
+ * Default implementation of {@link Logger} that safely writes the message into the console.
+ *
+ * @experimental
+ */
+export class ConsoleLogger implements Logger {
+  constructor(private _console: Console, private _debugEnabled: boolean = true) {}
+
+  log(...args: any[]): void { this._invokeConsoleMethod('log', args); }
+
+  info(...args: any[]): void { this._invokeConsoleMethod('info', args); }
+
+  warn(...args: any[]): void { this._invokeConsoleMethod('warn', args); }
+
+  error(...args: any[]): void { this._invokeConsoleMethod('error', args); }
+
+  debug(...args: any[]): void {
+    if (this._debugEnabled) this._invokeConsoleMethod('debug', args);
+  }
+
+  group(groupTitle?: string): void {
+    const args = groupTitle != null ? [groupTitle] : [];
+    this._invokeConsoleMethod('group', args);
+  }
+
+  groupEnd(): void { this._invokeConsoleMethod('groupEnd'); }
+
+  private _invokeConsoleMethod(type: string, args?: any[]): void {
+    let logFn: Function = (<any>this._console)[type] || this._console.log || noop;
+
+    // console methods in IE9 don't have 'apply' method, polyfill it
+    if (!logFn.apply) {
+      logFn = Function.prototype.bind.call(logFn, this._console);
+    }
+
+    logFn.apply(this._console, args);
+  }
+}
+
+/**
+ * No op implementation of {@link Logger}.
+ *
+ * @experimental
+ */
+export class NoOpLogger implements Logger {
+  log(): void {}
+
+  info(): void {}
+
+  warn(): void {}
+
+  error(): void {}
+
+  debug(): void {}
+
+  group(): void {}
+
+  groupEnd(): void {}
+}
diff --git a/modules/@angular/core/test/application_module_spec.ts b/modules/@angular/core/test/application_module_spec.ts
@@ -6,12 +6,47 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {LOCALE_ID} from '@angular/core';
+import {Injectable, LOCALE_ID} from '@angular/core';
+import {TestBed} from '@angular/core/testing';
+
+import {_loggerFactory} from '../src/application_module';
+import {ConsoleLogger, Logger, NoOpLogger} from '../src/logger';
 import {describe, expect, inject, it} from '../testing/testing_internal';
 
 export function main() {
   describe('Application module', () => {
     it('should set the default locale to "en-US"',
        inject([LOCALE_ID], (defaultLocale: string) => { expect(defaultLocale).toEqual('en-US'); }));
+
+    describe('Logger', () => {
+      describe('factory', () => {
+        it('should return NoOpLogger when disabled', () => {
+          const logger = _loggerFactory({enabled: false});
+          expect(logger instanceof NoOpLogger).toBe(true);
+        });
+
+        it('should return ConsoleLogger when enabled', () => {
+          const logger = _loggerFactory({enabled: true});
+          expect(logger instanceof ConsoleLogger).toBe(true);
+        });
+
+        it('should use isDevMode without options', () => {
+          const logger = _loggerFactory();
+          expect(logger instanceof ConsoleLogger).toBe(true);
+        });
+      });
+
+      describe('should inject Logger service', () => {
+        @Injectable()
+        class DependsOnLogger {
+          constructor(public logger: Logger) {}
+        }
+
+        beforeEach(() => TestBed.configureTestingModule({providers: [DependsOnLogger]}));
+
+        it('works',
+           () => expect(TestBed.get(DependsOnLogger).logger instanceof ConsoleLogger).toBe(true));
+      });
+    });
   });
 }
diff --git a/modules/@angular/core/test/logger_spec.ts b/modules/@angular/core/test/logger_spec.ts
@@ -0,0 +1,131 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {ConsoleLogger, Logger, NoOpLogger} from '../src/logger';
+
+interface TestConsole {
+  log?: (arg?: any) => string;
+  warn?: (arg?: any) => string;
+  info?: (arg?: any) => string;
+  error?: (arg?: any) => string;
+  debug?: (arg?: any) => string;
+  group?: (arg?: any) => string;
+  groupEnd?: (arg?: any) => string;
+}
+
+export function main() {
+  describe('Logger', () => {
+    let logBuffer: string;
+    let _console: TestConsole|any;
+
+    beforeEach(() => {
+      logBuffer = '';
+      _console = {
+        log: (arg: any = '') => logBuffer += `log${arg};`,
+        warn: (arg: any = '') => logBuffer += `warn${arg};`,
+        info: (arg: any = '') => logBuffer += `info${arg};`,
+        error: (arg: any = '') => logBuffer += `error${arg};`,
+        debug: (arg: any = '') => logBuffer += `debug${arg};`,
+        group: (arg: any = '') => logBuffer += `group${arg};`,
+        groupEnd: () => logBuffer += 'groupEnd;',
+      };
+    });
+
+    describe('No op', () => {
+      it('should not log anything', () => {
+        const logger: Logger = new NoOpLogger();
+        logger.info();
+        logger.log();
+        logger.debug();
+        logger.error();
+        logger.warn();
+        logger.group();
+        logger.groupEnd();
+        expect(logBuffer).toEqual('');
+      });
+    });
+
+    describe('Console', () => {
+      it('should use console if present', () => {
+        const logger: Logger = new ConsoleLogger(_console);
+        logger.info('$');
+        logger.log('$');
+        logger.debug('$');
+        logger.error('$');
+        logger.warn('$');
+        logger.group('$');
+        logger.groupEnd();
+        expect(logBuffer).toEqual('info$;log$;debug$;error$;warn$;group$;groupEnd;');
+      });
+
+      it('should use console.log() if other not present', () => {
+        const _console: any = {log: () => logBuffer += 'log;'};
+        const logger: Logger = new ConsoleLogger(_console);
+        logger.info();
+        logger.log();
+        logger.debug();
+        logger.error();
+        logger.warn();
+        logger.group();
+        logger.groupEnd();
+        expect(logBuffer).toEqual('log;log;log;log;log;log;log;');
+      });
+
+      it('should use noop if no console', () => {
+        const logger: Logger = new ConsoleLogger(<any>{});
+        logger.info();
+        logger.log();
+        logger.debug();
+        logger.error();
+        logger.warn();
+        logger.group();
+        logger.groupEnd();
+        expect(logBuffer).toEqual('');
+      });
+
+      describe('debug', () => {
+        it('should skip debugging output if disabled', () => {
+          const logger: Logger = new ConsoleLogger(_console, false);
+          logger.info();
+          logger.log();
+          logger.debug();
+          logger.error();
+          logger.warn();
+          logger.group();
+          logger.groupEnd();
+          expect(logBuffer).toEqual('info;log;error;warn;group;groupEnd;');
+        });
+      });
+
+      describe('IE logging', () => {
+        it(`should work in IE where console methods don't have 'apply' method`, () => {
+          removeApplyFunctionForIE(_console);
+          const logger: Logger = new ConsoleLogger(_console);
+          logger.info('$');
+          logger.log('$');
+          logger.debug('$');
+          logger.error('$');
+          logger.warn('$');
+          logger.group('$');
+          logger.groupEnd();
+          expect(logBuffer).toEqual('info$;log$;debug$;error$;warn$;group$;groupEnd;');
+        });
+
+        function removeApplyFunctionForIE(console: TestConsole): void {
+          console.log.apply = null;
+          console.warn.apply = null;
+          console.info.apply = null;
+          console.error.apply = null;
+          console.debug.apply = null;
+          console.group.apply = null;
+          console.groupEnd.apply = null;
+        }
+      });
+    });
+  });
+}
diff --git a/modules/@angular/core/testing/index.ts b/modules/@angular/core/testing/index.ts
@@ -19,3 +19,4 @@ export * from './test_bed';
 export * from './testing';
 export * from './metadata_override';
 export * from './private_export_testing';
+export * from './mock_logger';