perf(common): In case of an expensive log, allow to pass a function

packages/common/services/console-logger.service.ts

@@ -1,6 +1,11 @@
 import { Injectable, Optional } from '../decorators/core';
 import { clc, yellow } from '../utils/cli-colors.util';
-import { isPlainObject, isString, isUndefined } from '../utils/shared.utils';
+import {
+  isFunction,
+  isPlainObject,
+  isString,
+  isUndefined,
+} from '../utils/shared.utils';
 import { LoggerService, LogLevel } from './logger.service';
 import { isLogLevelEnabled } from './utils';
 
@@ -221,7 +226,10 @@ export class ConsoleLogger implements LoggerService {
   }
 
   protected stringifyMessage(message: unknown, logLevel: LogLevel) {
-    return isPlainObject(message) || Array.isArray(message)
+    // If the message is a function, call it and re-resolve its value.
+    return isFunction(message)
+      ? this.stringifyMessage(message(), logLevel)
+      : isPlainObject(message) || Array.isArray(message)
       ? `${this.colorize('Object:', logLevel)}\n${JSON.stringify(
           message,
           (key, value) =>

packages/common/test/services/logger.service.spec.ts

@@ -256,6 +256,34 @@ describe('Logger', () => {
       loggerWithContext.resetContext();
       expect(loggerWithContext['context']).to.equal('context');
     });
+
+    describe('functions for message', () => {
+      let processStdoutWriteSpy: sinon.SinonSpy;
+      const logger = new ConsoleLogger();
+      const message = 'Hello World';
+
+      beforeEach(() => {
+        processStdoutWriteSpy = sinon.spy(process.stdout, 'write');
+      });
+      afterEach(() => {
+        processStdoutWriteSpy.restore();
+      });
+
+      it('works', () => {
+        logger.log(() => message);
+
+        expect(processStdoutWriteSpy.calledOnce).to.be.true;
+        expect(processStdoutWriteSpy.firstCall.firstArg).to.include(message);
+        // Ensure we didn't serialize the function itself.
+        expect(processStdoutWriteSpy.firstCall.firstArg).not.to.include(' => ');
+        expect(processStdoutWriteSpy.firstCall.firstArg).not.to.include(
+          'function',
+        );
+        expect(processStdoutWriteSpy.firstCall.firstArg).not.to.include(
+          'Function',
+        );
+      });
+    });
   });
 
   describe('[instance methods]', () => {

packages/common/utils/shared.utils.ts

@@ -41,7 +41,8 @@ export const normalizePath = (path?: string): string =>
 export const stripEndSlash = (path: string) =>
   path[path.length - 1] === '/' ? path.slice(0, path.length - 1) : path;
 
-export const isFunction = (val: any): boolean => typeof val === 'function';
+export const isFunction = (val: any): val is Function =>
+  typeof val === 'function';
 export const isString = (val: any): val is string => typeof val === 'string';
 export const isNumber = (val: any): val is number => typeof val === 'number';
 export const isConstructor = (val: any): boolean => val === 'constructor';