Consider adding custom formatter that shows log line origin...

[chadacious]

One thing that I found difficult when using this package is not always easily knowing where my log messages were coming from. Perhaps you could provide in your readme a custom formatter that would show the source file and line number. Something like this:

        format(...parms) {
            const args = Array.prototype.slice.call(parms, [1]); // change arguments to an array, but drop the first item (log level)
            let out = `[${parms[0]}] ${JSON.stringify(new Date())} `;
            args.forEach((arg) => { out += ` ${util.inspect(arg)}`; });
            if ((process.env.LOG_ORIGIN || '').toLowerCase() === 'true') {
                try {
                    const err = new Error();
                    const callerLine = err.stack.split('\n')[3];
                    const index = callerLine.indexOf('at ');
                    const origin = callerLine.slice(index + 2, callerLine.length);
                    return `${out}\n\t${origin}`;
                } catch (e) { return `${out}`; }
            }
            return `${out}`;
        },

And a sample of the output with an env variable of LOG_ORIGIN=true would be:

[info] "2019-03-28T16:12:31.931Z"  'Prerequisite table LocalUser exists.'
         exports.checkPrerequisiteTable (C:/Projects/..../src/models/index.js:14:9)
[trace] "2019-03-28T16:13:02.159Z"  'the request user is' 'chad@....com'
         ApolloServer.context (C:/Projects/..../src/index.js:77:17)

[chadacious]

If your using this package in a browser, the way its working causes the console's output to show the line in the logger that does the console.log, again making it difficult to find the line that actually invoked the log statement.

A quick change to fix that could be to change this:

logger[level] = function(){
        var args = Array.prototype.slice.call(arguments);
        args.unshift(level);  // log level is added as the first parameter
        console.log(logger.format.apply(logger, args));
};

to this:

logger[level] = (function(){
        var args = Array.prototype.slice.call(arguments);
        args.unshift(level);  // log level is added as the first parameter
        return Function.prototype.bind.call(console.log, console, logger.format.apply(logger, args));
})();

This will show the source line that calls logger functions (e.g. things like log.trace) instead of just always showing the logger's console.log line.

I'm not sure how people tend to be using this package, but I should think this change would work in most scenarios.

[chadacious]

Actually, I didn't realize when I suggested the above that the bind would only be invoked once on initialization of the log functions. So if you have something in your format like say, a time value that is always changing, the above won't work because it will always show the same time.

So to get that scenario to work, you can change the last code block in my above comment to:

Object.defineProperty(logger, level, {
        get: function(){
            var args = Array.prototype.slice.call(arguments);
            args.unshift(level);  // log level is added as the first parameter
            return Function.prototype.bind.call(console.log, console, logger.format.apply(logger, args));
          }
      });

Thanks to this stackoverflow answer for that neat trick,