Is it possible to enable multiple plugins?

[kmiwa007]

First off, thank you @pimterry for creating loglevel! QQ, when writing plugins, is it possible to apply multiple plugins such that the next plugin has access to the reformatted message of the previous plugin?

ie. when following the example:

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

    return function (message) {
                                 ^^^ This is always the original raw message from the log call
        rawMethod("Newsflash: " + message);
    };
};
log.setLevel(log.getLevel()); 

Is there a pattern for accessing the reformatted message from a previous plugin?

Thanks!

[pimterry]

Hi @kmiwa007 - yes, it's actually easy, that code already does it! If you run that same code twice, every message will start with Newsflash: Newsflash: <msg> because the plugins combine.

Effectively what happens here is that if you apply this repeatedly then originalFactory will be the the factory from the last registered plugin, and so rawMethod will be the method built by that plugin, so when you call it, you're just chaining to that plugin. If you just repeat this code, the plugins will run in reverse order (most recently registered plugin first).

This is just JS itself providing this, the API isn't doing anything special at all. The only gotcha is that if you use the same originalFactory value from before the first plugin, then you'll replace it entirely.

Here's a quick demo:

const originalFactory1 = log.methodFactory;
log.methodFactory = function (methodName, logLevel, loggerName) {
    var rawMethod = originalFactory1(methodName, logLevel, loggerName);

    return function (message) {
        rawMethod("P1: " + message);
    };
};

const originalFactory2 = log.methodFactory;
log.methodFactory = function (methodName, logLevel, loggerName) {
    var rawMethod = originalFactory2(methodName, logLevel, loggerName);

    return function (message) {
        rawMethod("P2: " + message);
    };
};
log.setLevel(log.getLevel());

log.log("Hello world"); // Prints "P1: P2: Hello world"

The two plugins run in reverse order: the second plugin prepends "P2" - giving "P2: Hello world" - and then that gets passed to the the first plugin which prepends "P1", giving "P1: P2: Hello world".

Note that I've given the originalFactory vars different names to avoid collision here, but they could have the same names and live in different files/scopes and that'd be fine.

You can open https://pimterry.github.io/loglevel/demo/index.html and paste that into the browser console there to test this. Does that all make sense?

[kmiwa007]

the plugins will run in reverse order (most recently registered plugin first).

ah, that was the key concept. I see the updated message now. Thanks!