Logging in JavaScript (Cordova, Web) Applications

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This tutorial provides the required code snippets in order to add logging capabilities in JavaScript (Cordova, Web) applications.

Prerequisite: Make sure to read the overview of client-side log collection.

Enabling log capture

By default, log capture is enabled. Log capture saves logs to the client and can be enabled or disabled programmatically. Logs are sent to the server with an explicit send call, or with auto log

Note: Enabling log capture at verbose levels can impact the consumption of the device CPU, file system space, and the size of the payload when the client sends logs over the network.

To disable log capturing:


WL.Logger.config({capture: false});



Sending captured logs

Send logs to the MobileFirst according to your application’s logic. Auto log send can also be enabled to automatically send logs. If logs are not sent before the maximum size is reached, the log file is then purged in favor of newer logs.

Note: Adopt the following pattern when you collect log data. Sending data on an interval ensures that you are seeing your log data in near real-time in the MobileFirst Analytics Console.

Cordova apps

To ensure that all captured logs are sent, consider one of the following strategies:

  • Call the send method at a time interval.
  • Call the send method from within the app lifecycle event callbacks.
  • Increase the max file size of the persistent log buffer (in bytes):
    setInterval(function() {
    }, 60000);
WL.Logger.config({ maxFileSize: 150000 });

Web apps

setInterval(function() {
}, 60000);

The maximum file size for the Web API is 5 mb and cannot be changed.

Auto log sending

By default, auto log send is enabled. Each time a successful resource request is sent to the server, the captured logs are also sent, with a 60-second minimum interval between sends. Auto log send can be enabled or disabled from the client. By default auto log send is enabled.

For Cordova apps

To enable:

WL.Logger.config({autoSendLogs: true});

To disable:

WL.Logger.config({autoSendLogs: false});

For Web apps

To enable:


To disable:


Change autoSendLog interval

By default autoSendLog interval is set as 60 seconds. AutoSendLog interval can be changed using following method.

For Cordova apps

To set autoSendLog interval as 120 seconds, see the following snippet.

WL.Logger.config({autoSendLogs: true,autoSendLogsInterval: 120});

For Web apps

To set autoSendLog interval as 120 seconds, see the following snippet.

ibmmfpfanalytics.enableAutoSend(true, 120);

Fine-tuning with the Logger API

The MobileFirst client SDK makes internal use of the Logger API. By default, you are capturing log entries made by the SDK. To fine-tune log collection, use logger instances with package names. You can also control which logging level is captured by the analytics using server-side filters.

As an example to capture logs only where the level is ERROR for the myApp package name, follow these steps.

Fine-tuning Cordova apps

  1. Use a WL.Logger instance with the myApp package name.

    var logger = WL.Logger.create({ pkg: 'MyApp' });
  2. Optional: Specify a filter to restrict log capture and log output to only the specified level and package programmatically.

         filters: {
             'MyApp': 'ERROR'
  3. Optional: Control the filters remotely by fetching a server configuration profile.

Web apps

For the Web SDK the level cannot be set by the client. All logging is sent to the server until the configuration is changed by retrieving the server configuration profile.

Fetching server configuration profiles

Logging levels can be set by the client or by retrieving configuration profiles from the server. From the MobileFirst Analytics Console, a log level can be set globally (all logger instances) or for a specific package or packages. For information on configuring the filter from the MobileFirst Analytics Console, see Configuring log filters. For the client to fetch the configuration overrides that are set on the server, the updateConfigFromServer method must be called from a place in the code that is regularly run, such as in the app lifecycle callbacks.

Fetching server configuration profiles for Cordova apps


Fetching server configuration profiles for Web apps


Logging example

Outputs to a browser JavaScript console, LogCat, or Xcode console.

Logging example Cordova

var MathUtils = function(){
   var logger = WL.Logger.create({pkg: 'MathUtils'});
   var sum = function(a, b){
      var sum = a + b;
      logger.debug('sum called with args ' + a + ' and ' + b + '. Returning ' + sum);
      return sum;

Logging example Web

For logging with Web applications, use the preceding example and replace

var logger = WL.Logger.create({pkg: 'MathUtils'});


var logger = ibmmfpfanalytics.logger.create({pkg: 'MathUtils'});
Inclusive terminology note: The Mobile First Platform team is making changes to support the IBM® initiative to replace racially biased and other discriminatory language in our code and content with more inclusive language. While IBM values the use of inclusive language, terms that are outside of IBM's direct influence are sometimes required for the sake of maintaining user understanding. As other industry leaders join IBM in embracing the use of inclusive language, IBM will continue to update the documentation to reflect those changes.
Last modified on June 01, 2020