Allow lazy Logger execution (#103)

packages/util/src/logger.js

@@ -3,11 +3,18 @@
 // of the ISC license. See the LICENSE file for details.
 // @flow
 
-import type { Logger } from './types';
+import type { Logger, Logger$Data } from './types';
 
 type ConsoleType = 'error' | 'log' | 'warn';
 
-function apply (log: ConsoleType, type: string, values: Array<mixed>): void {
+const isFunction = require('./is/function');
+
+function apply (log: ConsoleType, type: string, values: Logger$Data): void {
+  if (values.length === 1 && isFunction(values[0])) {
+    // flowlint-next-line unclear-type:off
+    return apply(log, type, ((values[0]: any): Function)());
+  }
+
   console[log].apply(console, [new Date().toString(), type].concat(values));
 }
 
@@ -37,10 +44,10 @@ module.exports = function logger (_type: string): Logger {
 
   return {
     debug: isDebug
-      ? (...values: Array<mixed>): void => apply('log', type, values)
-      : (...values: Array<mixed>): void => void 0,
-    error: (...values: Array<mixed>): void => apply('error', type, values),
-    log: (...values: Array<mixed>): void => apply('log', type, values),
-    warn: (...values: Array<mixed>): void => apply('warn', type, values)
+      ? (...values: Logger$Data): void => apply('log', type, values)
+      : (...values: Logger$Data): void => void 0,
+    error: (...values: Logger$Data): void => apply('error', type, values),
+    log: (...values: Logger$Data): void => apply('log', type, values),
+    warn: (...values: Logger$Data): void => apply('warn', type, values)
   };
 };

packages/util/src/logger.spec.js

@@ -38,6 +38,38 @@ describe('logger', () => {
     jest.restoreAllMocks();
   });
 
+  it('logs to console.log with .log', () => {
+    l.log('console.log test');
+
+    expect(spy.log).toHaveBeenCalledWith(
+      dateMatch,
+      prefixMatch,
+      'console.log test'
+    );
+  });
+
+  it('logs with mulptiple values', () => {
+    l.log('test', 'a', 2);
+
+    expect(spy.log).toHaveBeenCalledWith(
+      dateMatch,
+      prefixMatch,
+      'test',
+      'a',
+      2
+    );
+  });
+
+  it('logs when called with function', () => {
+    l.log(() => 'a function test');
+
+    expect(spy.log).toHaveBeenCalledWith(
+      dateMatch,
+      prefixMatch,
+      'a function test'
+    );
+  });
+
   it('logs to console.error with .error', () => {
     l.error('console.error test');
 
@@ -58,28 +90,6 @@ describe('logger', () => {
     );
   });
 
-  it('logs to console.log with .log', () => {
-    l.log('console.log test');
-
-    expect(spy.log).toHaveBeenCalledWith(
-      dateMatch,
-      prefixMatch,
-      'console.log test'
-    );
-  });
-
-  it('logs to with mulptiple values', () => {
-    l.log('test', 'a', 2);
-
-    expect(spy.log).toHaveBeenCalledWith(
-      dateMatch,
-      prefixMatch,
-      'test',
-      'a',
-      2
-    );
-  });
-
   it('does debug log when DEBUG specified', () => {
     l.debug('test');
 

packages/util/src/types.js

@@ -10,9 +10,11 @@ export interface ExtErrorInterface {
   stack: string;
 }
 
+export type Logger$Data = Array<mixed | () => Array<mixed>>;
+
 export type Logger = {
-  debug: (...values: Array<mixed>) => void,
-  error: (...values: Array<mixed>) => void,
-  log: (...values: Array<mixed>) => void,
-  warn: (...values: Array<mixed>) => void
+  debug: (...values: Logger$Data) => void,
+  error: (...values: Logger$Data) => void,
+  log: (...values: Logger$Data) => void,
+  warn: (...values: Logger$Data) => void
 };