loglevel

If you are using TypeScript and want to use loglevel as a global variable, you must declare it manually.

1. Create a loglevel.d.ts file.
2. Ensure the file is included in your build (via tsconfig.json include, command line, or a triple-slash reference).
3. Add the following content to loglevel.d.ts:

import * as log from 'loglevel';
export as namespace log;
export = log;

In an AMD environment, define loglevel as a dependency in your module definition.

define(['loglevel'], function(log) {
   log.warn("dangerously convenient");
});

Since loglevel is a UMD module, different bundlers/transpilers may require different import syntaxes.

For most tools, use the default import:

import log from 'loglevel';
log.warn("module-tastic");

If that doesn't work for your environment, try a wildcard import:

import * as log from 'loglevel';
log.warn("module-tastic");

In a CommonJS environment like Node.js, require the module to access the logging object.

var log = require('loglevel');
log.warn("unreasonably simple");

You can include loglevel directly in your HTML by using a <script> tag pointing to the minified file.

<script src="loglevel.min.js"></script>
<script>
log.warn("too easy");
</script>

To install loglevel using npm, run the following command in your terminal:

npm install loglevel

Use log.setLevel(level, [persist]) to disable all logging below the specified level.

Arguments:

• level: Can be a log level name (e.g., 'error', 'warn', 'info', 'debug', 'trace', or 'silent'), a numeric index from 0 (trace) to 5 (silent), or a value from the internal log.levels list (e.g., log.levels.SILENT) for type safety.
• persist (optional): A boolean. If true (default), the level is saved to LocalStorage or cookies. If false, persistence is skipped.

You can extend loglevel by redefining log.methodFactory. This function is called for each enabled method whenever the log level is set. It should return a function that performs the actual logging.

To maintain the original functionality and stacktrace reliability, it is recommended to wrap the existing log.methodFactory rather than replacing it entirely.

Important: After redefining log.methodFactory, you must call log.rebuild() to apply the changes.

var originalFactory = log.methodFactory;
log.methodFactory = function (methodName, logLevel, loggerName) {
    var rawMethod = originalFactory(methodName, logLevel, loggerName);

    return function (message) {
        rawMethod("Newsflash: " + message);
    };
};
log.rebuild(); // Be sure to call the rebuild method in order to apply plugin.

If another library is already using the log global variable, call log.noConflict() immediately after loading loglevel. This restores the original value of the log global and returns the loglevel instance, which you can assign to a different variable name.

<script src="loglevel.min.js"></script>
<script>
var logging = log.noConflict();

logging.warn("still pretty easy");
</script>

Use log.getLevel() to return the current logging level as a number from 0 (trace) to 5 (silent). This is useful for optimizing performance by checking if expensive data generation is required before logging.

if (log.getLevel() <= log.levels.DEBUG) {
  var logData = runExpensiveDataGeneration();
  log.debug(logData);
}