Updated the files.

my-app/node_modules/log4js/lib/appenders/multiFile.js

@@ -0,0 +1,91 @@
+const debug = require('debug')('log4js:multiFile');
+const path = require('path');
+const fileAppender = require('./file');
+
+const findFileKey = (property, event) =>
+  event[property] || event.context[property];
+
+module.exports.configure = (config, layouts) => {
+  debug('Creating a multi-file appender');
+  const files = new Map();
+  const timers = new Map();
+
+  function checkForTimeout(fileKey) {
+    const timer = timers.get(fileKey);
+    const app = files.get(fileKey);
+    /* istanbul ignore else: failsafe */
+    if (timer && app) {
+      if (Date.now() - timer.lastUsed > timer.timeout) {
+        debug('%s not used for > %d ms => close', fileKey, timer.timeout);
+        clearInterval(timer.interval);
+        timers.delete(fileKey);
+        files.delete(fileKey);
+        app.shutdown((err) => {
+          if (err) {
+            debug('ignore error on file shutdown: %s', err.message);
+          }
+        });
+      }
+    } else {
+      // will never get here as files and timers are coupled to be added and deleted at same place
+      debug('timer or app does not exist');
+    }
+  }
+
+  const appender = (logEvent) => {
+    const fileKey = findFileKey(config.property, logEvent);
+    debug('fileKey for property ', config.property, ' is ', fileKey);
+    if (fileKey) {
+      let file = files.get(fileKey);
+      debug('existing file appender is ', file);
+      if (!file) {
+        debug('creating new file appender');
+        config.filename = path.join(config.base, fileKey + config.extension);
+        file = fileAppender.configure(config, layouts);
+        files.set(fileKey, file);
+        if (config.timeout) {
+          debug('creating new timer');
+          timers.set(fileKey, {
+            timeout: config.timeout,
+            lastUsed: Date.now(),
+            interval: setInterval(
+              checkForTimeout.bind(null, fileKey),
+              config.timeout
+            ),
+          });
+        }
+      } else if (config.timeout) {
+        debug('%s extending activity', fileKey);
+        timers.get(fileKey).lastUsed = Date.now();
+      }
+
+      file(logEvent);
+    } else {
+      debug('No fileKey for logEvent, quietly ignoring this log event');
+    }
+  };
+
+  appender.shutdown = (cb) => {
+    let shutdownFunctions = files.size;
+    if (shutdownFunctions <= 0) {
+      cb();
+    }
+    let error;
+    timers.forEach((timer, fileKey) => {
+      debug('clearing timer for ', fileKey);
+      clearInterval(timer.interval);
+    });
+    files.forEach((app, fileKey) => {
+      debug('calling shutdown for ', fileKey);
+      app.shutdown((err) => {
+        error = error || err;
+        shutdownFunctions -= 1;
+        if (shutdownFunctions <= 0) {
+          cb(error);
+        }
+      });
+    });
+  };
+
+  return appender;
+};