Implement custom logger interface based on console methods

EmilianoSanchez · EmilianoSanchez · commit 77a56de39de8 · 2025-09-10T13:48:59.000-03:00
diff --git a/src/logger/__tests__/index.spec.ts b/src/logger/__tests__/index.spec.ts
@@ -16,12 +16,10 @@ test('SPLIT LOGGER / isLogLevelString utility function', () => {
   expect(isLogLevelString(LOG_LEVELS.DEBUG)).toBe(true); // Calling isLogLevelString should return true with a LOG_LEVELS value
   expect(isLogLevelString('ERROR')).toBe(true); // Calling isLogLevelString should return true with a string equal to some LOG_LEVELS value
   expect(isLogLevelString('INVALID LOG LEVEL')).toBe(false); // Calling isLogLevelString should return false with a string not equal to any LOG_LEVELS value
-
 });
 
 test('SPLIT LOGGER / LogLevels exposed mappings', () => {
   expect(LogLevels).toEqual(LOG_LEVELS); // Exposed log levels should contain the levels we want.
-
 });
 
 test('SPLIT LOGGER / Logger class shape', () => {
@@ -94,27 +92,22 @@ function testLogLevels(levelToTest: SplitIO.LogLevel) {
 
   // Restore spied object.
   consoleLogSpy.mockRestore();
-
 }
 
 test('SPLIT LOGGER / Logger class public methods behavior - instance.debug', () => {
   testLogLevels(LogLevels.DEBUG);
-
 });
 
 test('SPLIT LOGGER / Logger class public methods behavior - instance.info', () => {
   testLogLevels(LogLevels.INFO);
-
 });
 
 test('SPLIT LOGGER / Logger class public methods behavior - instance.warn', () => {
   testLogLevels(LogLevels.WARN);
-
 });
 
 test('SPLIT LOGGER / Logger class public methods behavior - instance.error', () => {
   testLogLevels(LogLevels.ERROR);
-
 });
 
 test('SPLIT LOGGER / _sprintf', () => {
diff --git a/src/logger/index.ts b/src/logger/index.ts
@@ -41,23 +41,31 @@ const defaultOptions = {
   prefix: 'splitio',
   logLevel: LogLevels.NONE,
   showLevel: true,
-  logger(formattedMsg: string) { console.log(formattedMsg); }
+};
+
+const defaultConsoleLogger: SplitIO.Logger = {
+  debug(message: string) { console.log(message); },
+  info(message: string) { console.log(message); },
+  warn(message: string) { console.log(message); },
+  error(message: string) { console.log(message); }
 };
 
 export class Logger implements ILogger {
 
   private options: Required<ILoggerOptions>;
   private codes: Map<number, string>;
   private logLevel: number;
+  private logger: SplitIO.Logger;
 
   constructor(options?: ILoggerOptions, codes?: Map<number, string>) {
     this.options = objectAssign({}, defaultOptions, options);
     this.codes = codes || new Map();
     this.logLevel = LogLevelIndexes[this.options.logLevel];
+    this.logger = defaultConsoleLogger;
   }
 
-  setLogger(logger: (formattedMsg: string, level: SplitIO.LogLevel, msg: string) => void) {
-    this.options.logger = logger;
+  setLogger(logger: SplitIO.Logger) {
+    this.logger = logger;
   }
 
   setLogLevel(logLevel: SplitIO.LogLevel) {
@@ -66,32 +74,30 @@ export class Logger implements ILogger {
   }
 
   debug(msg: string | number, args?: any[]) {
-    if (this._shouldLog(LogLevelIndexes.DEBUG)) this._log(LogLevels.DEBUG, msg, args);
+    if (this._shouldLog(LogLevelIndexes.DEBUG)) this.logger.debug(this._log(LogLevels.DEBUG, msg, args));
   }
 
   info(msg: string | number, args?: any[]) {
-    if (this._shouldLog(LogLevelIndexes.INFO)) this._log(LogLevels.INFO, msg, args);
+    if (this._shouldLog(LogLevelIndexes.INFO)) this.logger.info(this._log(LogLevels.INFO, msg, args));
   }
 
   warn(msg: string | number, args?: any[]) {
-    if (this._shouldLog(LogLevelIndexes.WARN)) this._log(LogLevels.WARN, msg, args);
+    if (this._shouldLog(LogLevelIndexes.WARN)) this.logger.warn(this._log(LogLevels.WARN, msg, args));
   }
 
   error(msg: string | number, args?: any[]) {
-    if (this._shouldLog(LogLevelIndexes.ERROR)) this._log(LogLevels.ERROR, msg, args);
+    if (this._shouldLog(LogLevelIndexes.ERROR)) this.logger.error(this._log(LogLevels.ERROR, msg, args));
   }
 
-  private _log(level: SplitIO.LogLevel, msg: string | number, args?: any[]) {
+  private _log(level: SplitIO.LogLevel, msg: string | number, args?: any[]): string {
     if (typeof msg === 'number') {
       const format = this.codes.get(msg);
       msg = format ? _sprintf(format, args) : `Message code ${msg}${args ? ', with args: ' + args.toString() : ''}`;
     } else {
       if (args) msg = _sprintf(msg, args);
     }
 
-    const formattedText = this._generateLogMessage(level, msg);
-
-    this.options.logger(formattedText, level, msg);
+    return this._generateLogMessage(level, msg);
   }
 
   private _generateLogMessage(level: SplitIO.LogLevel, text: string) {
diff --git a/src/logger/types.ts b/src/logger/types.ts
@@ -4,11 +4,10 @@ export interface ILoggerOptions {
   prefix?: string;
   logLevel?: SplitIO.LogLevel;
   showLevel?: boolean; // @TODO remove this param eventually since it is not being set `false` anymore
-  logger?: (formattedMsg: string, level: SplitIO.LogLevel, msg: string) => void;
 }
 
 export interface ILogger extends SplitIO.ILogger {
-  setLogger(logger: (formattedMsg: string, level: SplitIO.LogLevel, msg: string) => void): void;
+  setLogger(logger: SplitIO.Logger): void;
 
   debug(msg: any): void;
   debug(msg: string | number, args?: any[]): void;
diff --git a/src/utils/settingsValidation/logger/__tests__/index.spec.ts b/src/utils/settingsValidation/logger/__tests__/index.spec.ts
@@ -3,6 +3,13 @@ import { loggerMock, getLoggerLogLevel } from '../../../../logger/__tests__/sdkL
 import { validateLogger as pluggableValidateLogger } from '../pluggableLogger';
 import { validateLogger as builtinValidateLogger } from '../builtinLogger';
 
+const customLogger = {
+  debug: jest.fn(),
+  info: jest.fn(),
+  warn: jest.fn(),
+  error: jest.fn()
+};
+
 const testTargets = [
   [pluggableValidateLogger],
   [builtinValidateLogger]
@@ -11,7 +18,10 @@ const testTargets = [
 describe('logger validators', () => {
 
   const consoleLogSpy = jest.spyOn(global.console, 'log');
-  afterEach(() => { consoleLogSpy.mockClear(); });
+  afterEach(() => {
+    consoleLogSpy.mockClear();
+    customLogger.error.mockClear();
+  });
 
   test.each(testTargets)('returns a NONE logger if `debug` property is not defined or false', (validateLogger) => { // @ts-ignore
     expect(getLoggerLogLevel(validateLogger({}))).toBe('NONE');
@@ -24,15 +34,16 @@ describe('logger validators', () => {
   test.each(testTargets)('returns a NONE logger if `debug` property is invalid and logs the error', (validateLogger) => {
     expect(getLoggerLogLevel(validateLogger({ debug: null }))).toBe('NONE');
     expect(getLoggerLogLevel(validateLogger({ debug: 10 }))).toBe('NONE');
-    expect(getLoggerLogLevel(validateLogger({ debug: {} }))).toBe('NONE');
+    expect(getLoggerLogLevel(validateLogger({ debug: {}, logger: customLogger }))).toBe('NONE');
 
     if (validateLogger === builtinValidateLogger) {
       // for builtinValidateLogger, a logger cannot be passed as `debug` property
       expect(getLoggerLogLevel(validateLogger({ debug: loggerMock }))).toBe('NONE');
-      expect(consoleLogSpy).toBeCalledTimes(4);
-    } else {
       expect(consoleLogSpy).toBeCalledTimes(3);
+    } else {
+      expect(consoleLogSpy).toBeCalledTimes(2);
     }
+    expect(customLogger.error).toBeCalledTimes(1);
   });
 
   test.each(testTargets)('returns a logger with the provided log level if `debug` property is true or a string log level', (validateLogger) => {
diff --git a/src/utils/settingsValidation/logger/builtinLogger.ts b/src/utils/settingsValidation/logger/builtinLogger.ts
@@ -3,7 +3,7 @@ import { ILogger } from '../../../logger/types';
 import { isLocalStorageAvailable } from '../../env/isLocalStorageAvailable';
 import { isNode } from '../../env/isNode';
 import { codesDebug } from '../../../logger/messages/debug';
-import { getLogLevel } from './commons';
+import { getLogLevel, isLogger } from './commons';
 import SplitIO from '../../../../types/splitio';
 
 const allCodes = new Map(codesDebug);
@@ -46,10 +46,10 @@ export function validateLogger(settings: { debug: unknown, logger?: unknown }):
   const logLevel: SplitIO.LogLevel | undefined = debug !== undefined ? getLogLevel(debug) : initialLogLevel;
 
   const log = new Logger({ logLevel: logLevel || initialLogLevel }, allCodes);
-  if (typeof logger === 'function') log.setLogger(logger as (formattedMsg: string, level: SplitIO.LogLevel, msg: string) => void);
+  if (isLogger(logger)) log.setLogger(logger);
 
   // @ts-ignore // if logLevel is undefined at this point, it means that settings `debug` value is invalid
-  if (!logLevel) log._log(LogLevels.ERROR, 'Invalid Log Level - No changes to the logs will be applied.');
+  if (!logLevel) log.logger.error(log._log(LogLevels.ERROR, 'Invalid Log Level - No changes to the logs will be applied.'));
 
   return log;
 }
diff --git a/src/utils/settingsValidation/logger/commons.ts b/src/utils/settingsValidation/logger/commons.ts
@@ -18,3 +18,7 @@ export function getLogLevel(debugValue: unknown): SplitIO.LogLevel | undefined {
       debugValue :
       undefined;
 }
+
+export function isLogger(log: any): log is SplitIO.Logger {
+  return log !== null && typeof log === 'object' && typeof log.debug === 'function' && typeof log.info === 'function' && typeof log.warn === 'function' && typeof log.error === 'function';
+}
diff --git a/src/utils/settingsValidation/logger/pluggableLogger.ts b/src/utils/settingsValidation/logger/pluggableLogger.ts
@@ -1,10 +1,10 @@
 import { Logger, LogLevels } from '../../../logger';
 import { ILogger } from '../../../logger/types';
 import SplitIO from '../../../../types/splitio';
-import { getLogLevel } from './commons';
+import { getLogLevel, isLogger } from './commons';
 
-function isLogger(log: any): log is ILogger {
-  return log !== null && typeof log === 'object' && typeof log.debug === 'function' && typeof log.info === 'function' && typeof log.warn === 'function' && typeof log.error === 'function' && typeof log.setLogLevel === 'function';
+function isILogger(log: any): log is ILogger {
+  return isLogger(log) && typeof (log as any).setLogLevel === 'function';
 }
 
 // By default it starts disabled.
@@ -22,18 +22,18 @@ export function validateLogger(settings: { debug: unknown, logger?: unknown }):
   let logLevel: SplitIO.LogLevel | undefined = initialLogLevel;
 
   if (debug !== undefined) {
-    if (isLogger(debug)) {
-      if (typeof logger === 'function') debug.setLogger(logger as (formattedMsg: string, level: SplitIO.LogLevel, msg: string) => void);
+    if (isILogger(debug)) {
+      if (isLogger(logger)) debug.setLogger(logger);
       return debug;
     }
     logLevel = getLogLevel(settings.debug);
   }
 
   const log = new Logger({ logLevel: logLevel || initialLogLevel });
-  if (typeof logger === 'function') log.setLogger(logger as (formattedMsg: string, level: SplitIO.LogLevel, msg: string) => void);
+  if (isLogger(logger)) log.setLogger(logger);
 
   // @ts-ignore // `debug` value is invalid if logLevel is undefined at this point
-  if (!logLevel) log._log(LogLevels.ERROR, 'Invalid `debug` value at config. Logs will be disabled.');
+  if (!logLevel) log.logger.error(log._log(LogLevels.ERROR, 'Invalid `debug` value at config. Logs will be disabled.'));
 
   return log;
 }
diff --git a/types/splitio.d.ts b/types/splitio.d.ts
@@ -91,7 +91,7 @@ interface ISharedSettings {
    * Do not change these settings unless you're working an advanced use case, like connecting to the Split proxy.
    */
   urls?: SplitIO.UrlSettings;
-  logger?: (formattedMsg: string, level: SplitIO.LogLevel, msg: string) => void;
+  logger?: SplitIO.Logger;
 }
 /**
  * Common settings properties for SDKs with synchronous API (standalone and localhost modes).
@@ -564,7 +564,7 @@ declare namespace SplitIO {
       telemetry: string;
     };
     readonly integrations?: IntegrationFactory[];
-    readonly logger?: (formattedMsg: string, level: SplitIO.LogLevel, msg: string) => void;
+    readonly logger?: Logger;
     readonly debug: boolean | LogLevel | ILogger;
     readonly version: string;
     /**
@@ -595,6 +595,15 @@ declare namespace SplitIO {
    * Log levels.
    */
   type LogLevel = 'DEBUG' | 'INFO' | 'WARN' | 'ERROR' | 'NONE';
+  /**
+   * Custom logger interface.
+   */
+  interface Logger {
+    debug(message: string): any;
+    info(message: string): any;
+    warn(message: string): any;
+    error(message: string): any;
+  }
   /**
    * Logger API
    */

Original file line number	Diff line number	Diff line change
`@@ -18,3 +18,7 @@ export function getLogLevel(debugValue: unknown): SplitIO.LogLevel \| undefined {`
`18`	`18`	`debugValue :`
`19`	`19`	`undefined;`
`20`	`20`	`}`
	`21`	`+`
	`22`	`+export function isLogger(log: any): log is SplitIO.Logger {`
	`23`	`+ return log !== null && typeof log === 'object' && typeof log.debug === 'function' && typeof log.info === 'function' && typeof log.warn === 'function' && typeof log.error === 'function';`
	`24`	`+}`