Update eslint config.

Taking advantage of the new LogMessageFormatter return type, the
ConsoleLogAppender logs the formatted message as-is if it is a string,
but when processing structured data inserts a string summary consisting
of the message level, scope, and message summary or method. The full
object is still logged to the console as well for inspection.

.gitignore

@@ -1,2 +1,5 @@
 node_modules/
+dist/
 *.sw?
+.lvimrc
+jdbernard-logging-*.tgz

README.md

@@ -0,0 +1,166 @@
+# Overview
+
+`@jdbernard/logging` implements a simple but powerful logging system for
+JavaScript applications based on the idea of heirarchical loggers. It heavily
+inspired by the usage patterns of [log4j][], [logback][], and similar tools in other
+ecosystems.
+
+## Getting Started
+
+Install the package from npm:
+```bash
+npm install @jdbernard/logging
+```
+
+Then, in your application, you can use the logging system like so:
+
+```typescript
+import { logService, ConsoleAppender, LogLevel } from '@jdbernard/logging';
+
+logService.ROOT_LOGGER.appenders.push(new ConsoleAppender(LogLevel.INFO));
+const logger = logService.getLogger('example');
+
+logger.info('Starting application');
+```
+
+## Loggers and Appenders
+
+The logging system is composed of two main components: loggers and appenders.
+Loggers are used to create log events, which are then passed to the appenders
+associated with the logger and it's parent. An appender is a function that
+takes a log event and writes it to some destination, such as the console, a
+file, or a network socket. Appenders also have a logging level threshold, which
+determines which log events are acted upon by the appender.
+
+Loggers are hierarchical, with the hierarchy defined by the logger name. When a
+log message is generated on a *Logger*, it is sent to any appenders associated
+with that logger, and then triggered on the parent logger, being sent to any of
+the parent logger's appenders, and so on up the hierarchy. Similarly, when a
+logging event is generated, it is filtered by the effective logging level of
+the logger. If there is no threshold set on the logger, the effective logging
+level is inherited from the parent logger. This pattern is explained in detail
+in the [logback documentation][effective logging level] and applies in the same
+manner to this library.
+
+Together, the cascading effective logging threshold and the upward propogation
+of log events to parent appenders allows for simple yet fine-grained control
+over the logging output of an application.
+
+## Layouts
+
+One difference from other logging libraries is the absense of layouts. Layouts
+are used in many logging libraries to format the log message before it is
+written to the appender. This requires the assumption of all logs being written
+to a text-based destination, which is not always the case for us.
+
+In this library, all logs are internally stored as structured data, defined by
+the *LogMessage* interface. Notably, the *message* field can be either a string
+or an object, allowing for the addition of arbitrary fields to be added to the
+log event.
+
+The concept of Layouts still has a place, but it has been moved to be an
+implementation detail of the appenders. *ConsoleAppender* accepts a
+*LogMessageFormatter* function allowing for formatting of the resulting
+messages written to the console. the *ApiAppender* would be an example of an
+appender for which layout would be irrelevant.
+
+Finally, notice that all of the appenders provided by this library
+automatically persist log messages as structured data, flattening the `message`
+field if it is an object. *ConsoleAppender* will write the log message as a
+JSON object, promoting fields in the `message` object to top-level fields in
+the output. For example:
+
+```typescript
+import { logService, ConsoleAppender } from '@jdbernard/logging';
+
+logService.ROOT_LOGGER.appenders.push(new ConsoleAppender('TRACE'));
+const logger = logService.getLogger('example');
+
+function someBusinessLogic() {
+  logger.debug({ method: 'someBusinessLogic', msg: 'Doing some business logic', foo: 'bar' });
+}
+
+logger.info('Starting application');
+someBusinessLogic();
+```
+
+results in the following two events logged as output to the console:
+
+```json
+{"timestamp":"2021-09-01T00:00:00.000Z","level":"INFO","scope":"example","message":"Starting application"}
+{"timestamp":"2021-09-01T00:00:00.000Z","level":"DEBUG","scope":"example","msg":"Doing some business logic","method":"someBusinessLogic","foo":"bar"}
+```
+
+Note that the field name in the structured data for string messages is
+"message". In the case of an object message, the fields are used as provided.
+Fields defined on the *LogMessage* interface are reserved and should not be
+used as keys in the message object (and will be ignored if they are). So, for
+example:
+
+```typescript
+logger.debug({ level: 'WARN', message: 'Example of ignored fields', timestamp: 'today' });
+
+results in the following event logged as output to the console (note the
+ignored `level` and `timestamp` fields from the object):
+
+```json
+{"timestamp":"2021-09-01T00:00:00.000Z","level":"DEBUG","scope":"example","message":"Example of ignored fields"}
+```
+
+This flattening behavior is implemented in the `flattenMessage` function
+exported from the `@jdbernard/logging/log-message.ts` module and is available
+for use in custom appender implemetations.
+
+As a final note, the *ConsoleAppender* has some special behavior for the ERROR
+level and *stacktrace* field when running in a web browser to take advantage of
+the console's built-in. See the documentation for the *ConsoleAppender* for
+more information.
+
+## Worked Example
+
+To illustrate the usage of the logging system and the purpose of the
+fine-grained control described above, consider the following TypeScript
+example:
+
+```typescript
+// main.ts -- Entry point of the application
+// A console appender is attached to the root logger to log all events at or
+// above the INFO level.
+logService.ROOT_LOGGER.appenders.push(new ConsoleAppender(LogLevel.INFO));
+
+// An API appender is attached to the root logger to forward all ERROR events
+// to a server-side error log collector.
+logServive.ROOT_LOGGER.appenders.push(new ApiAppender(
+  'https://api.example.com/error-logs',
+  appStore.user.sessionToken,
+  LogLevel.ERROR));
+
+const appLog = logService.getLogger('app');
+appLog.info('Starting application');
+
+// api.ts -- API implementaiton
+const apiLog = logService.getLogger('app/api');
+
+// http-client.ts -- HTTP client implementation
+const httpLog = logService.getLogger('app/api/http-client');
+```
+
+Because different parts of the application use namespaced loggers, we can
+dynamically adjust the logging level of different parts of the application
+without changing the code. For example, to increase the logging level of the
+HTTP client to DEBUG, we can add the following line to the `main.ts` file:
+
+```typescript
+logService.getLogger('app/api/http-client').setLevel(LogLevel.DEBUG);
+```
+
+Additionally, if, for some reason, we only wanted to forward the ERROR events
+from the API namespace to the server-side error log collector, we could attach
+the *ApiAppender* to the `app/api` logger instead of the root logger. This
+would allow us to log all events from both the API and HTTP client loggers to
+the API log collector, but ignore the rest of the application regardless of the
+logging level.
+
+[log4j]: https://logging.apache.org/log4j/2.x/
+[logback]: https://logback.qos.ch/
+[effective logging level]: https://logback.qos.ch/manual/architecture.html#effectiveLevel

dist/api-log-appender.d.ts

@@ -1,18 +0,0 @@
-import { LogMessage, LogLevel } from './log-message';
-import LogAppender from './log-appender';
-export declare class ApiLogAppender implements LogAppender {
-    readonly apiEndpoint: string;
-    authToken?: string | undefined;
-    batchSize: number;
-    minimumTimePassedInSec: number;
-    maximumTimePassedInSec: number;
-    threshold: LogLevel;
-    private http;
-    private msgBuffer;
-    private lastSent;
-    constructor(apiEndpoint: string, authToken?: string | undefined, threshold?: LogLevel);
-    appendMessage(msg: LogMessage): void;
-    private doPost;
-    private checkPost;
-}
-export default ApiLogAppender;

dist/api-log-appender.js

@@ -1,60 +0,0 @@
-"use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.ApiLogAppender = void 0;
-const axios_1 = require("axios");
-const log_message_1 = require("./log-message");
-class ApiLogAppender {
-    constructor(apiEndpoint, authToken, threshold) {
-        this.apiEndpoint = apiEndpoint;
-        this.authToken = authToken;
-        this.batchSize = 10;
-        this.minimumTimePassedInSec = 60;
-        this.maximumTimePassedInSec = 120;
-        this.threshold = log_message_1.LogLevel.ALL;
-        this.http = axios_1.default.create();
-        this.msgBuffer = [];
-        this.lastSent = 0;
-        this.checkPost = () => {
-            const now = Date.now();
-            const min = this.lastSent + this.minimumTimePassedInSec * 1000;
-            const max = this.lastSent + this.maximumTimePassedInSec * 1000;
-            if ((this.msgBuffer.length >= this.batchSize && min < now) ||
-                (this.msgBuffer.length > 0 && max < now)) {
-                this.doPost();
-            }
-            setTimeout(this.checkPost, Math.max(10000, this.minimumTimePassedInSec * 1000));
-        };
-        setTimeout(this.checkPost, 1000);
-        if (threshold) {
-            this.threshold = threshold;
-        }
-    }
-    appendMessage(msg) {
-        if (this.threshold && msg.level < this.threshold) {
-            return;
-        }
-        this.msgBuffer.push({
-            level: log_message_1.LogLevel[msg.level],
-            message: typeof msg.message === 'string'
-                ? msg.message
-                : JSON.stringify(msg.message),
-            scope: msg.scope,
-            stacktrace: msg.stacktrace,
-            timestamp: msg.timestamp.toISOString()
-        });
-    }
-    doPost() {
-        if (this.msgBuffer.length > 0 && this.authToken) {
-            this.http.post(this.apiEndpoint, this.msgBuffer, {
-                headers: {
-                    'Content-Type': 'application/json',
-                    Authorization: `Bearer ${this.authToken}`
-                }
-            });
-            this.lastSent = Date.now();
-            this.msgBuffer = [];
-        }
-    }
-}
-exports.ApiLogAppender = ApiLogAppender;
-exports.default = ApiLogAppender;

dist/console-log-appender.d.ts

@@ -1,8 +0,0 @@
-import { LogMessage, LogLevel } from './log-message';
-import LogAppender from './log-appender';
-export declare class ConsoleLogAppender implements LogAppender {
-    threshold: LogLevel;
-    constructor(threshold?: LogLevel);
-    appendMessage(msg: LogMessage): void;
-}
-export default ConsoleLogAppender;

dist/console-log-appender.js

@@ -1,54 +0,0 @@
-"use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.ConsoleLogAppender = void 0;
-/*tslint:disable:no-console*/
-const log_message_1 = require("./log-message");
-class ConsoleLogAppender {
-    constructor(threshold) {
-        this.threshold = log_message_1.LogLevel.ALL;
-        if (threshold) {
-            this.threshold = threshold;
-        }
-    }
-    appendMessage(msg) {
-        if (this.threshold && msg.level < this.threshold) {
-            return;
-        }
-        let logMethod = console.log;
-        switch (msg.level) {
-            case log_message_1.LogLevel.ALL:
-                logMethod = console.log;
-                break;
-            case log_message_1.LogLevel.TRACE:
-                logMethod = console.log;
-                break;
-            case log_message_1.LogLevel.DEBUG:
-                logMethod = console.debug;
-                break;
-            case log_message_1.LogLevel.LOG:
-                logMethod = console.log;
-                break;
-            case log_message_1.LogLevel.INFO:
-                logMethod = console.info;
-                break;
-            case log_message_1.LogLevel.WARN:
-                logMethod = console.warn;
-                break;
-            case log_message_1.LogLevel.ERROR:
-            case log_message_1.LogLevel.FATAL:
-                logMethod = console.trace;
-                break;
-        }
-        if (msg.error) {
-            logMethod(`[${msg.scope}]:`, msg.message, msg.error);
-        }
-        else if (msg.stacktrace) {
-            logMethod(`[${msg.scope}]:`, msg.message, msg.stacktrace);
-        }
-        else {
-            logMethod(`[${msg.scope}]:`, msg.message);
-        }
-    }
-}
-exports.ConsoleLogAppender = ConsoleLogAppender;
-exports.default = ConsoleLogAppender;

dist/index.d.ts

@@ -1,6 +0,0 @@
-export * from './log-message';
-export * from './log-appender';
-export * from './log-service';
-export * from './console-log-appender';
-export * from './api-log-appender';
-export * from './logger';

dist/index.js

@@ -1,18 +0,0 @@
-"use strict";
-var __createBinding = (this && this.__createBinding) || (Object.create ? (function(o, m, k, k2) {
-    if (k2 === undefined) k2 = k;
-    Object.defineProperty(o, k2, { enumerable: true, get: function() { return m[k]; } });
-}) : (function(o, m, k, k2) {
-    if (k2 === undefined) k2 = k;
-    o[k2] = m[k];
-}));
-var __exportStar = (this && this.__exportStar) || function(m, exports) {
-    for (var p in m) if (p !== "default" && !exports.hasOwnProperty(p)) __createBinding(exports, m, p);
-};
-Object.defineProperty(exports, "__esModule", { value: true });
-__exportStar(require("./log-message"), exports);
-__exportStar(require("./log-appender"), exports);
-__exportStar(require("./log-service"), exports);
-__exportStar(require("./console-log-appender"), exports);
-__exportStar(require("./api-log-appender"), exports);
-__exportStar(require("./logger"), exports);

dist/log-appender.d.ts

@@ -1,5 +0,0 @@
-import { LogLevel, LogMessage } from './log-message';
-export default interface LogAppender {
-    threshold: LogLevel;
-    appendMessage(message: LogMessage): void;
-}

dist/log-appender.js

@@ -1,2 +0,0 @@
-"use strict";
-Object.defineProperty(exports, "__esModule", { value: true });

dist/log-message.d.ts

@@ -1,19 +0,0 @@
-export declare enum LogLevel {
-    ALL = 0,
-    TRACE = 1,
-    DEBUG = 2,
-    LOG = 3,
-    INFO = 4,
-    WARN = 5,
-    ERROR = 6,
-    FATAL = 7
-}
-export interface LogMessage {
-    scope: string;
-    level: LogLevel;
-    message: string | object;
-    stacktrace: string;
-    error?: Error;
-    timestamp: Date;
-}
-export default LogMessage;

dist/log-message.js

@@ -1,14 +0,0 @@
-"use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.LogLevel = void 0;
-var LogLevel;
-(function (LogLevel) {
-    LogLevel[LogLevel["ALL"] = 0] = "ALL";
-    LogLevel[LogLevel["TRACE"] = 1] = "TRACE";
-    LogLevel[LogLevel["DEBUG"] = 2] = "DEBUG";
-    LogLevel[LogLevel["LOG"] = 3] = "LOG";
-    LogLevel[LogLevel["INFO"] = 4] = "INFO";
-    LogLevel[LogLevel["WARN"] = 5] = "WARN";
-    LogLevel[LogLevel["ERROR"] = 6] = "ERROR";
-    LogLevel[LogLevel["FATAL"] = 7] = "FATAL";
-})(LogLevel = exports.LogLevel || (exports.LogLevel = {}));

dist/log-service.d.ts

@@ -1,10 +0,0 @@
-import { LogLevel } from './log-message';
-import Logger from './logger';
-export declare class LogService {
-    private loggers;
-    get ROOT_LOGGER(): Logger;
-    constructor();
-    getLogger(name: string, threshold?: LogLevel): Logger;
-}
-export declare const logService: LogService;
-export default logService;

dist/log-service.js

@@ -1,35 +0,0 @@
-"use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.logService = exports.LogService = void 0;
-const log_message_1 = require("./log-message");
-const logger_1 = require("./logger");
-const ROOT_LOGGER_NAME = 'ROOT';
-class LogService {
-    constructor() {
-        this.loggers = {};
-        this.loggers[ROOT_LOGGER_NAME] = new logger_1.default(ROOT_LOGGER_NAME, undefined, log_message_1.LogLevel.ALL);
-    }
-    get ROOT_LOGGER() {
-        return this.loggers[ROOT_LOGGER_NAME];
-    }
-    getLogger(name, threshold) {
-        if (this.loggers[name]) {
-            return this.loggers[name];
-        }
-        let parentLogger;
-        const parentLoggerName = Object.keys(this.loggers)
-            .filter((n) => name.startsWith(n))
-            .reduce((acc, cur) => (acc.length > cur.length ? acc : cur), '');
-        if (parentLoggerName) {
-            parentLogger = this.loggers[parentLoggerName];
-        }
-        else {
-            parentLogger = this.ROOT_LOGGER;
-        }
-        this.loggers[name] = parentLogger.createChildLogger(name, threshold);
-        return this.loggers[name];
-    }
-}
-exports.LogService = LogService;
-exports.logService = new LogService();
-exports.default = exports.logService;

dist/logger.d.ts

@@ -1,23 +0,0 @@
-import { LogMessage, LogLevel } from './log-message';
-import LogAppender from './log-appender';
-export declare type DeferredMsg = () => string | object;
-export declare type MessageType = string | DeferredMsg | object;
-export declare class Logger {
-    readonly name: string;
-    private parentLogger?;
-    threshold?: LogLevel | undefined;
-    appenders: LogAppender[];
-    constructor(name: string, parentLogger?: Logger | undefined, threshold?: LogLevel | undefined);
-    createChildLogger(name: string, threshold?: LogLevel): Logger;
-    doLog(level: LogLevel, message: Error | MessageType, stacktrace?: string): void;
-    trace(message: Error | MessageType, stacktrace?: string): void;
-    debug(message: Error | MessageType, stacktrace?: string): void;
-    log(message: MessageType, stacktrace?: string): void;
-    info(message: MessageType, stacktrace?: string): void;
-    warn(message: MessageType, stacktrace?: string): void;
-    error(message: Error | MessageType, stacktrace?: string): void;
-    fatal(message: Error | MessageType, stacktrace?: string): void;
-    protected sendToAppenders(logMsg: LogMessage): void;
-    protected getEffectiveThreshold(): LogLevel;
-}
-export default Logger;

dist/logger.js

@@ -1,88 +0,0 @@
-"use strict";
-Object.defineProperty(exports, "__esModule", { value: true });
-exports.Logger = void 0;
-const log_message_1 = require("./log-message");
-class Logger {
-    constructor(name, parentLogger, threshold) {
-        this.name = name;
-        this.parentLogger = parentLogger;
-        this.threshold = threshold;
-        this.appenders = [];
-    }
-    createChildLogger(name, threshold) {
-        return new Logger(name, this, threshold);
-    }
-    doLog(level, message, stacktrace) {
-        if (level < this.getEffectiveThreshold()) {
-            return;
-        }
-        const logMsg = {
-            scope: this.name,
-            level,
-            message: '',
-            stacktrace: '',
-            timestamp: new Date()
-        };
-        if (message === undefined || message === null) {
-            logMsg.message = message;
-            logMsg.stacktrace = stacktrace == null ? '' : stacktrace;
-        }
-        else if (message.call !== undefined) {
-            logMsg.message = message();
-            logMsg.stacktrace = stacktrace == null ? '' : stacktrace;
-        }
-        else if (message instanceof Error) {
-            const error = message;
-            logMsg.error = error;
-            logMsg.message = `${error.name}: ${error.message}`;
-            logMsg.stacktrace = error.stack == null ? '' : error.stack;
-        }
-        else {
-            // string | object
-            logMsg.message = message;
-            logMsg.stacktrace = stacktrace == null ? '' : stacktrace;
-        }
-        this.sendToAppenders(logMsg);
-    }
-    trace(message, stacktrace) {
-        this.doLog(log_message_1.LogLevel.TRACE, message, stacktrace);
-    }
-    debug(message, stacktrace) {
-        this.doLog(log_message_1.LogLevel.DEBUG, message, stacktrace);
-    }
-    log(message, stacktrace) {
-        this.doLog(log_message_1.LogLevel.LOG, message, stacktrace);
-    }
-    info(message, stacktrace) {
-        this.doLog(log_message_1.LogLevel.INFO, message, stacktrace);
-    }
-    warn(message, stacktrace) {
-        this.doLog(log_message_1.LogLevel.WARN, message, stacktrace);
-    }
-    error(message, stacktrace) {
-        this.doLog(log_message_1.LogLevel.ERROR, message, stacktrace);
-    }
-    fatal(message, stacktrace) {
-        this.doLog(log_message_1.LogLevel.FATAL, message, stacktrace);
-    }
-    sendToAppenders(logMsg) {
-        this.appenders.forEach(app => {
-            app.appendMessage(logMsg);
-        });
-        if (this.parentLogger) {
-            this.parentLogger.sendToAppenders(logMsg);
-        }
-    }
-    getEffectiveThreshold() {
-        if (this.threshold) {
-            return this.threshold;
-        }
-        if (this.parentLogger) {
-            return this.parentLogger.getEffectiveThreshold();
-        }
-        // should never happen (root logger should always have a threshold
-        return log_message_1.LogLevel.ALL;
-    }
-}
-exports.Logger = Logger;
-exports.default = Logger;

eslint.config.mjs

@@ -0,0 +1,68 @@
+import importPlugin from 'eslint-plugin-import'
+import tsParser from '@typescript-eslint/parser'
+import eslintJs from '@eslint/js'
+import eslintTs from 'typescript-eslint'
+
+const tsFiles = ['src/**/*.ts']
+
+const customTypescriptConfig = {
+  files: tsFiles,
+  plugins: {
+    import: importPlugin,
+    'import/parsers': tsParser,
+  },
+  languageOptions: {
+    parser: tsParser,
+    parserOptions: {
+      project: './tsconfig.json',
+    },
+  },
+  settings: {
+    'import/parsers': {
+      '@typescript-eslint/parser': ['.ts'],
+    },
+  },
+  rules: {
+    'linebreak-style': ['error', 'unix'],
+    quotes: ['error', 'single', { avoidEscape: true }],
+    semi: ['error', 'never'],
+    '@typescript-eslint/no-unused-vars': ['error', {
+      'args': 'all',
+      'argsIgnorePattern': '^_',
+      'caughtErrorsIgnorePattern': '^_',
+      'destructuredArrayIgnorePattern': '^_',
+      'varsIgnorePattern': '^_',
+    }],
+  },
+}
+
+const recommendedTypeScriptConfigs = [
+  ...eslintTs.configs.recommended.map((config) => ({
+    ...config,
+    files: tsFiles,
+  })),
+  ...eslintTs.configs.stylistic.map((config) => ({
+    ...config,
+    files: tsFiles,
+  })),
+]
+
+export default [
+  {
+    ignores: [
+      'docs/*',
+      'build/*',
+      'lib/*',
+      'dist/*',
+    ],
+  }, // global ignores
+  eslintJs.configs.recommended,
+  ...recommendedTypeScriptConfigs,
+  customTypescriptConfig,
+  {
+    rules: {
+      quotes: ['error', 'single', { avoidEscape: true }],
+      semi: ['error', 'never'],
+    },
+  },
+]

package-lock.json

@@ -1,43 +0,0 @@
-{
-  "name": "js-log",
-  "version": "1.0.0",
-  "lockfileVersion": 1,
-  "requires": true,
-  "dependencies": {
-    "axios": {
-      "version": "0.19.2",
-      "resolved": "https://registry.npmjs.org/axios/-/axios-0.19.2.tgz",
-      "integrity": "sha512-fjgm5MvRHLhx+osE2xoekY70AhARk3a6hkN+3Io1jc00jtquGvxYlKlsFUhmUET0V5te6CcZI7lcv2Ym61mjHA==",
-      "requires": {
-        "follow-redirects": "1.5.10"
-      }
-    },
-    "debug": {
-      "version": "3.1.0",
-      "resolved": "https://registry.npmjs.org/debug/-/debug-3.1.0.tgz",
-      "integrity": "sha512-OX8XqP7/1a9cqkxYw2yXss15f26NKWBpDXQd0/uK/KPqdQhxbPa994hnzjcE2VqQpDslf55723cKPUOGSmMY3g==",
-      "requires": {
-        "ms": "2.0.0"
-      }
-    },
-    "follow-redirects": {
-      "version": "1.5.10",
-      "resolved": "https://registry.npmjs.org/follow-redirects/-/follow-redirects-1.5.10.tgz",
-      "integrity": "sha512-0V5l4Cizzvqt5D44aTXbFZz+FtyXV1vrDN6qrelxtfYQKW0KO0W2T/hkE8xvGa/540LkZlkaUjO4ailYTFtHVQ==",
-      "requires": {
-        "debug": "=3.1.0"
-      }
-    },
-    "ms": {
-      "version": "2.0.0",
-      "resolved": "https://registry.npmjs.org/ms/-/ms-2.0.0.tgz",
-      "integrity": "sha1-VgiurfwAvmwpAd9fmGF4jeDVl8g="
-    },
-    "typescript": {
-      "version": "3.9.7",
-      "resolved": "https://registry.npmjs.org/typescript/-/typescript-3.9.7.tgz",
-      "integrity": "sha512-BLbiRkiBzAwsjut4x/dsibSTB6yWpwT5qWmC2OfuCg3GgVQCSgMs4vEctYPhsaGtd0AeuuHMkjZ2h2WG8MSzRw==",
-      "dev": true
-    }
-  }
-}

package.json

@@ -1,10 +1,15 @@
 {
   "name": "@jdbernard/logging",
-  "version": "1.1.0",
+  "version": "2.0.0",
   "description": "Simple Javascript logging service.",
-  "main": "src/index.ts",
-  "module": "dist/index.js",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
+  "files": [
+    "/dist"
+  ],
   "scripts": {
+    "build": "tsc",
+    "prepare": "npm run build",
     "test": "echo \"Error: no test specified\" && exit 1"
   },
   "repository": {
@@ -18,9 +23,9 @@
   "author": "Jonathan Bernard",
   "license": "GPL-3.0",
   "devDependencies": {
-    "typescript": "^3.9.7"
-  },
-  "dependencies": {
-    "axios": "^0.19.2"
+    "@typescript-eslint/parser": "^8.19.0",
+    "eslint-plugin-import": "^2.31.0",
+    "typescript": "^5.0.4",
+    "typescript-eslint": "^8.19.0"
   }
 }

src/api-log-appender.ts

@@ -1,23 +1,13 @@
-import Axios from 'axios';
+import { LogMessage, LogLevel, flattenMessage, FlattenedLogMessage } from './log-message';
+import { LogAppender } from './log-appender';
 
-import { LogMessage, LogLevel } from './log-message';
-import LogAppender from './log-appender';
-
-interface ApiMessage {
-  level: string;
-  message: string;
-  scope: string;
-  stacktrace: string;
-  timestamp: string;
-}
 export class ApiLogAppender implements LogAppender {
   public batchSize = 10;
   public minimumTimePassedInSec = 60;
   public maximumTimePassedInSec = 120;
   public threshold = LogLevel.ALL;
 
-  private http = Axios.create();
-  private msgBuffer: ApiMessage[] = [];
+  private msgBuffer: FlattenedLogMessage[] = [];
   private lastSent = 0;
 
   constructor(
@@ -36,21 +26,15 @@ export class ApiLogAppender implements LogAppender {
       return;
     }
 
-    this.msgBuffer.push({
-      level: LogLevel[msg.level],
-      message:
-        typeof msg.message === 'string'
-          ? msg.message
-          : JSON.stringify(msg.message),
-      scope: msg.scope,
-      stacktrace: msg.stacktrace,
-      timestamp: msg.timestamp.toISOString()
-    });
+    this.msgBuffer.push(flattenMessage(msg));
   }
 
   private doPost() {
     if (this.msgBuffer.length > 0 && this.authToken) {
-      this.http.post(this.apiEndpoint, this.msgBuffer, {
+      fetch(this.apiEndpoint, {
+        method: 'POST',
+        mode: 'cors',
+        body: JSON.stringify(this.msgBuffer),
         headers: {
           'Content-Type': 'application/json',
           Authorization: `Bearer ${this.authToken}`

src/console-log-appender.ts

@@ -1,14 +1,33 @@
-/*tslint:disable:no-console*/
-import { LogMessage, LogLevel } from './log-message';
-import LogAppender from './log-appender';
+import {
+  flattenMessage,
+  LogLevel,
+  LogMessage,
+  LogMessageFormatter,
+} from "./log-message";
+import { LogAppender } from "./log-appender";
 
+/**
+ * A log appender that writes log messages to the console. The behavior of the
+ * log appender can be configured with a threshold level and a message
+ * formatter.
+ *
+ * When the message formatter returns a string value, that value is logged to
+ * the console as-is. When the message formatter returns an object, a summary
+ * string is logged to the console, followed by the object itself. This allows
+ * logs to be easily read in the console, while still providing the structured
+ * data for inspection in the browser's developer tools.
+ */
 export class ConsoleLogAppender implements LogAppender {
   public threshold = LogLevel.ALL;
+  public formatter: LogMessageFormatter = flattenMessage;
 
-  constructor(threshold?: LogLevel) {
+  constructor(threshold?: LogLevel, formatter?: LogMessageFormatter) {
     if (threshold) {
       this.threshold = threshold;
     }
+    if (formatter) {
+      this.formatter = formatter;
+    }
   }
 
   public appendMessage(msg: LogMessage): void {
@@ -19,17 +38,13 @@ export class ConsoleLogAppender implements LogAppender {
     let logMethod = console.log;
     switch (msg.level) {
       case LogLevel.ALL:
-        logMethod = console.log;
-        break;
       case LogLevel.TRACE:
+      case LogLevel.LOG:
         logMethod = console.log;
         break;
       case LogLevel.DEBUG:
         logMethod = console.debug;
         break;
-      case LogLevel.LOG:
-        logMethod = console.log;
-        break;
       case LogLevel.INFO:
         logMethod = console.info;
         break;
@@ -42,12 +57,25 @@ export class ConsoleLogAppender implements LogAppender {
         break;
     }
 
-    if (msg.error) {
-      logMethod(`[${msg.scope}]:`, msg.message, msg.error);
-    } else if (msg.stacktrace) {
-      logMethod(`[${msg.scope}]:`, msg.message, msg.stacktrace);
+    const fmtMsg = this.formatter(msg);
+
+    if (typeof fmtMsg === "string") {
+      if (msg.error || msg.stacktrace) {
+        logMethod(fmtMsg, msg.error ?? msg.stacktrace);
+      } else {
+        logMethod(fmtMsg);
+      }
     } else {
-      logMethod(`[${msg.scope}]:`, msg.message);
+      const { message, _error, _stacktrace, ...rest } = fmtMsg;
+      const summary = `${LogLevel[msg.level]} -- ${msg.scope}: ${
+        message ?? fmtMsg.method
+      }\n`;
+
+      if (msg.error || msg.stacktrace) {
+        logMethod(summary, msg.error ?? msg.stacktrace, rest);
+      } else {
+        logMethod(summary, rest);
+      }
     }
   }
 }

src/log-appender.ts

@@ -1,5 +1,8 @@
 import { LogLevel, LogMessage } from './log-message';
-export default interface LogAppender {
+
+export interface LogAppender {
   threshold: LogLevel;
   appendMessage(message: LogMessage): void;
 }
+
+export default LogAppender;

src/log-message.ts

@@ -1,3 +1,5 @@
+import { omit } from './util'
+
 export enum LogLevel {
   ALL = 0,
   TRACE,
@@ -6,15 +8,15 @@ export enum LogLevel {
   INFO,
   WARN,
   ERROR,
-  FATAL
+  FATAL,
 }
 
-const kv = 'WARN';
-const TEST = LogLevel[kv];
-
-export function parseLogLevel(str: string, defaultLevel = LogLevel.INFO): LogLevel {
-  if (Object.prototype.hasOwnProperty.call(LogLevel, str)) {
-    return LogLevel[<any>str] as unknown as LogLevel;
+export function parseLogLevel(
+  str: string,
+  defaultLevel = LogLevel.INFO,
+): LogLevel {
+  if (str in LogLevel) {
+    return LogLevel[str as keyof typeof LogLevel] as LogLevel;
   } else {
     return defaultLevel;
   }
@@ -23,10 +25,60 @@ export function parseLogLevel(str: string, defaultLevel = LogLevel.INFO): LogLev
 export interface LogMessage {
   scope: string;
   level: LogLevel;
-  message: string | object;
-  stacktrace: string;
+  message: string | Record<string, unknown>;
+  stacktrace?: string;
   error?: Error;
   timestamp: Date;
 }
 
+export type FlattenedLogMessage = Record<string, unknown>;
+
+/**
+ * Flatten a log message to a plain object. The *message* field can be either a
+ * string or an object. In the case of an object message, the LogMessage should
+ * be flattened before being emitted by an appender, promoting the object's
+ * fields to the top level of the message. Fields defined on the *LogMessage*
+ * interface are reserved and should not be used as keys in the message object
+ * (and will be ignored if they are).
+ *
+ * So, for example:
+ *
+ * ```typescript
+ * const logger = logService.getLogger('example');
+ * logger.info({ foo: 'bar', baz: 'qux', timestamp: 'today', level: LogLevel.WARN });
+ * ```
+ *
+ * Should result after flattening in a structured log message like:
+ * ```json
+ * {"scope":"example","level":"INFO","foo":"bar","baz":"qux","timestamp":"2020-01-01T00:00:00.000Z"}
+ * ```
+ */
+export function flattenMessage(msg: LogMessage): FlattenedLogMessage {
+  if (typeof msg.message === 'string') {
+    return { ...msg, level: LogLevel[msg.level] };
+  } else {
+    const { message, ...rest } = msg;
+    return {
+      ...omit(message, [
+        'scope',
+        'level',
+        'stacktrace',
+        'error',
+        'timestamp',
+      ]),
+      ...rest,
+      level: LogLevel[msg.level],
+    };
+  }
+}
+export type LogMessageFormatter = (msg: LogMessage) => string | FlattenedLogMessage;
+
+export function structuredLogMessageFormatter(msg: LogMessage): string {
+  return JSON.stringify(flattenMessage(msg));
+}
+
+export function simpleTextLogMessageFormatter(msg: LogMessage): string {
+  return `[${msg.scope}] - ${msg.level}: ${msg.message}`;
+}
+
 export default LogMessage;

src/log-service.ts

@@ -1,10 +1,16 @@
 import { LogLevel } from './log-message';
-import Logger from './logger';
+import { Logger } from './logger';
 
 const ROOT_LOGGER_NAME = 'ROOT';
 
+/**
+ * Service for managing loggers. A LogService instance defines
+ * the service context for a set of loggers. Typically there is only one
+ * LogService instance per application, the one exported as default from this
+ * module.
+ */
 export class LogService {
-  private loggers: { [key: string]: Logger };
+  private loggers: Record<string, Logger>;
 
   public get ROOT_LOGGER() {
     return this.loggers[ROOT_LOGGER_NAME];
@@ -15,10 +21,38 @@ export class LogService {
     this.loggers[ROOT_LOGGER_NAME] = new Logger(
       ROOT_LOGGER_NAME,
       undefined,
-      LogLevel.ALL
+      LogLevel.ALL,
     );
   }
 
+  /**
+   * Get a logger by name. If the logger does not exist, it will be created.
+   * Loggers are hierarchical, with the heirarchy defined by the logger name.
+   * When creating a new logger, the parent logger is determined by the longest
+   * existing logger name that is a prefix of the new logger name. For example,
+   * if a logger with the name "foo" already exists, any subsequent loggers
+   * with the names "foo.bar", "foo/bar", "foolish.choice", etc. will be
+   * created as children of the "foo" logger.
+   *
+   * As another example, given the following invocations:
+   *
+   * ```typescript
+   * logService.getLogger('foo');
+   * logService.getLogger('foo.bar');
+   * logService.getLogger('foo.bar.baz');
+   * logService.getLogger('foo.qux');
+   * ```
+   *
+   * will result in the following logging hierarchy:
+   *
+   *     foo
+   *     ├─foo.bar
+   *     │ └─foo.bar.baz
+   *     └─foo.qux
+   *
+   * See the Logger class for details on how loggers are used and the
+   * implications of the logger hierarchy.
+   */
   public getLogger(name: string, threshold?: LogLevel): Logger {
     if (this.loggers[name]) {
       return this.loggers[name];
@@ -30,7 +64,7 @@ export class LogService {
       .filter((n: string) => name.startsWith(n))
       .reduce(
         (acc: string, cur: string) => (acc.length > cur.length ? acc : cur),
-        ''
+        '',
       );
 
     if (parentLoggerName) {

src/logger.ts

@@ -1,16 +1,52 @@
-import { LogMessage, LogLevel } from './log-message';
-import LogAppender from './log-appender';
+import { LogLevel, LogMessage } from './log-message';
+import { LogAppender } from './log-appender';
 
-export type DeferredMsg = () => string | object;
-export type MessageType = string | DeferredMsg | object;
+export type DeferredMsg = () => string | Record<string, unknown>;
+export type MessageType = string | DeferredMsg | Record<string, unknown>;
 
+export function isDeferredMsg(msg: MessageType): msg is DeferredMsg {
+  return typeof msg === 'function';
+}
+
+/**
+ * Logger class for logging messages.
+ *
+ * Loggers are used to log messages at different levels. The levels are, in
+ * order of increasing severity: TRACE, DEBUG, LOG, INFO, WARN, ERROR, FATAL.
+ * Log messages can be logged at a specific level by calling the corresponding
+ * method on the logger instance. For example, to log a message at the INFO
+ * level, call the *info* method on the logger.
+ *
+ * Loggers have a threshold level, which is the minimum level of log message
+ * that will be logged by the logger. Log messages with a level below the
+ * threshold will be ignored. The threshold level can be set when creating a
+ * logger, or by calling the *setThreshold* method on an existing logger. If a
+ * threshold is not set, the logger will use the threshold of its parent
+ * logger.
+ *
+ * Loggers are hierarchical, with the hierarchy defined by the logger name.
+ * The heirarchy is tracked by the children: child loggers have a link to their
+ * parents, while parent loggers do not have a list of their children.
+ *
+ * When a log message is logged by a logger, it is sent to all of the appenders
+ * attached to the logger and to the parent logger. Appenders can be attached
+ * to any Logger instance, but, because of this upwards propogation, appenders
+ * are usually attached to the root logger, which is an ancestor of all loggers
+ * created by the same LogService instance.
+ *
+ * Loggers are typically created and managed by a LogService instance.  The
+ * *LogService#getLogger* method is used to get a logger by name, creating it
+ * if necessary. When creating a new logger, the parent logger is determined by
+ * the longest existing logger name that is a prefix of the new logger name.
+ * For more details, see *LogService#getLogger*.
+ */
 export class Logger {
   public appenders: LogAppender[] = [];
 
   public constructor(
     public readonly name: string,
     private parentLogger?: Logger,
-    public threshold?: LogLevel
+    public threshold?: LogLevel,
   ) {}
 
   public createChildLogger(name: string, threshold?: LogLevel): Logger {
@@ -20,7 +56,7 @@ export class Logger {
   public doLog(
     level: LogLevel,
     message: Error | MessageType,
-    stacktrace?: string
+    stacktrace?: string,
   ): void {
     if (level < this.getEffectiveThreshold()) {
       return;
@@ -31,20 +67,20 @@ export class Logger {
       level,
       message: '',
       stacktrace: '',
-      timestamp: new Date()
+      timestamp: new Date(),
     };
 
     if (message === undefined || message === null) {
       logMsg.message = message;
-      logMsg.stacktrace = stacktrace == null ? '' : stacktrace;
-    } else if ((message as DeferredMsg).call !== undefined) {
-      logMsg.message = (message as DeferredMsg)();
-      logMsg.stacktrace = stacktrace == null ? '' : stacktrace;
+      logMsg.stacktrace = stacktrace ?? '';
     } else if (message instanceof Error) {
       const error = message as Error;
       logMsg.error = error;
       logMsg.message = `${error.name}: ${error.message}`;
-      logMsg.stacktrace = error.stack == null ? '' : error.stack;
+      logMsg.stacktrace = stacktrace ?? error.stack ?? '';
+    } else if (isDeferredMsg(message)) {
+      logMsg.message = message();
+      logMsg.stacktrace = stacktrace == null ? '' : stacktrace;
     } else {
       // string | object
       logMsg.message = message;
@@ -83,7 +119,7 @@ export class Logger {
   }
 
   protected sendToAppenders(logMsg: LogMessage) {
-    this.appenders.forEach(app => {
+    this.appenders.forEach((app) => {
       app.appendMessage(logMsg);
     });
 

src/util.ts

@@ -0,0 +1,12 @@
+export function omit(
+  obj: Record<string, unknown>,
+  keys: string[],
+): Record<string, unknown> {
+  const result: Record<string, unknown> = {};
+  for (const key in obj) {
+    if (!keys.includes(key)) {
+      result[key] = obj[key];
+    }
+  }
+  return result;
+}

tsconfig.json

@@ -1,10 +1,11 @@
 {
   "compilerOptions": {
     "module": "commonjs",
-    "target": "es6",
+    "target": "es2016",
     "declaration": true,
     "outDir": "./dist",
-    "strict": true
+    "strict": true,
+    "skipLibCheck": true
   },
   "include": [
     "src/**/*"