The below demo provides You code samples to write a console log using the UI5 Log API, which can be turned on/off on demand when using UI5 applications.

Developing a framework for UI5 can benefit from switchable logs, especially at the initial phase, or during troubleshooting. The demand and purpose can of course vary to utilize logging.

I did my first kick based on this great blog.

Technical summary

I believe code talks 🙂, but I would never let You without some base explanation about key facts when using the UI5 Log API.

• By default only errors are written to the Log by the API, even if You call the API (in JavaScript) to log a warning message in the console.
  You have to increase the log level to record log entries with lower severity, like warning(2), info(3) or debug(4)…
  Increasing the level will result in writing all the log entries with all previous levels. So if You set Log level to Debug(4), then Info(3) and Warning(2) messages will be written to the log as well.
• You can explicitly set the log level by one of the following methods:
  • using the URL parameter sap-ui-logLevel=<iLogLevel>
  • programmatically in JS: Log.setLevel(<iLogLevel>)
    Hint: to switch the log level, You can use this statement in the console during debugging as well 😉
  • If You have an index.html, set the following property in the UI5 bootstrap script:
    data-sap-ui-loglevel=”debug”
    All the existing log levels are enumerated in: sap/base/Log.Level
• You can increase the log level implicitly:
  • when url parameter sap-ui-debug=true is set, log level is increased automatically to debug(4)
• You can dump complete JS Objects to the console using the standard UI5 Log API, check out function logAnObject

Below You find a UI5 controller with several sample functions to create console log entries. The whole runnable UI5 demo project/application is available at: https://github.com/attilaberencsi/ui5logsamples.

Do not forget to select the required log levels to be shown by the browser console. One thing is successfully writing a log entry to the console, another one is that the browser is configured to display it.

Samples to write a Log

sap.ui.define([
        "sap/ui/core/mvc/Controller",
        "sap/base/Log"
    ],
    /**
     * @param {typeof sap.ui.core.mvc.Controller} Controller
     * Samples to log messages in the console, and to set the maximum log level (type of console messages Error/Warning(2)/Info(3)/Debug(4)...the level 
     * until including all previous levels they are written to the console.
     * 
     * The Log Level can be set by following ways:
     * - using the URL parameter sap-ui-logLevel=<logLevel>
     * - if You have an index.html, You can set the following property in the UI5 bootstrap script as well:  data-sap-ui-loglevel="debug" forex
     *   (all the existing log levels are enumareated in: sap/base/Log.Level)
     * - programatically: Log.setLevel(4). You can use this statement in the console during debugging as well, to switch the log level
     * 
     * HINT: do not forget to select the required messages types to be shown in the browser console settings of the developer tools.
     * 
     * Beside below examples: You can also use  sap/base/Log.setLevel to set log level programmatically for dedicated components only (not globally).
     * Detailed documentation of log API at https://sapui5.hana.ondemand.com/#/api/module:sap/base/Log
     */
    function (Controller, Log) {
        "use strict";

        return Controller.extend("com.sapdev.demo.log.ui5consolelog.controller.Log", {
            /**
             * Using variables can be helpful for console log messages, especially when You implement a framework
             */
            onInit: function () {
                this._sInfo = "Logging is available since 1.58";
                this._sShowInfoinConsole = "set URL parameter: sap-ui-logLevel=3";
            },

            /**
             * Error Messages are logged to the console always, callstack is included by default.
             */
            onLogError: function () {
                try {
                    let a = b;
                } catch (error) {
                    var sErrorDetails = error.toString();
                    Log.error(`SAPDEV: An error occured while executing this function`, `${sErrorDetails}`);
                }
            },

            /**
             * Wanrning messages are NOT written to the console by default, and contain no callstack. 
             * Add URL parameter  sap-ui-logLevel=2  to see them in the console foer example.
             * You can add some prefix like SAPDEV: to find Your log entries easier.
             */
            onLogWarning: function () {
                Log.warning("SAPDEV: Hi this is a Warning message", `Here comes the long description, like ${this._sInfo}`);
            },

            /**
             * Info messages are not whown by default, it requires to increase log level to 3 forex adding URL parameter  sap-ui-logLevel=3  to see them in the console.
             * You can add some prefix like SAPDEV: to find Your log entries easier.
             */
            onLogInfo: function () {
                // You can use this statement programatically, or in the console as well to set the required Log level (:
                Log.setLevel(3);
                Log.info(`SAPDEV: Hi this is an INFO message, to see it ${this._sShowInfoinConsole}`, `Here comes the long description, like ${this._sInfo}`);
            },

            /**
             * Debug messages include call stack and are logged to the console when url parameter  sap-ui-debug=true  is set, 
             * or the log level is increased to 4. 
             * The UI5 logger will then  dump error/warning/info messages as well.
             */
            onLogDebug: function () {
                //Log.setLevel(4);
                Log.debug(`SAPDEV: Hi this is an DEBUG message`, "Bla bla");
            },

            /**  
             * You can dump complete JS Objects as well.
             * Open Developer Tools / Console
             * Activate Support Assistant with with:  Ctrl + Alt+ Shift + P or use function  Log.logSupportInfo(true)  programatically.
             * Attention: The Object is dumped only if the above criterion are fullfilled ! 
             */
            logAnObject: function () {
                Log.setLevel(4);
                Log.logSupportInfo(true); // OR open Support Assistant with:  Ctrl + Alt+ Shift + P
                var oObject = {
                    Mamma: "Mia",
                    Donna: "Clara",
                    Mizeria: [1, 2, 3],
                    Items: [{
                        Apa: "Cuka",
                        Funda: "Luka"
                    }, {
                        Apa: "Kave",
                        Funda: "Duka"
                    }]
                };
                Log.debug(`SAPDEV: Hi this is an DEBUG message`, "with Support Info and Object Details", "", () => oObject);
            }

        });
    });

Screenshots

Closing Note

I’d like to emphasize that this is just writing the log to the browser console, but the API provides You options to collect log records. So You can display it on a UI, or send it somewhere 😉