Is it possible to bind a date/time to a console log?

Question

I have the following code:

var myLog = console.log.bind(console, '[DEBUG]');

Which works find when I want to log things prepended with [DEBUG] to the console. Now I want to add a date/time to the log and I tried this:

var myLog = console.log.bind(console, '[DEBUG ' + (new Date) + ']');

Which obviously does not work because it always logs the same time (the time that the .bind was called).

Is there any way (using .bind) to log the current time on each log without having to do this:

var myLog = function(){
    var args = ['[DEBUG ' + (new Date) + ']'];
    for(var i = 0; i < arguments.length; ++i) {
        args.push(arguments[i]);
    }
    return console.log.apply(console, args);
};

?

Because the above method shows me the line that console.log.apply was called and not the line that myLog was called.

Answer 1

Yes. http://jsfiddle.net/SwFJg/6/

var DEBUG = (function(){
    var timestamp = function(){};
    timestamp.toString = function(){
        return "[DEBUG " + (new Date).toLocaleTimeString() + "]";    
    };

    return {
        log: console.log.bind(console, '%s', timestamp)
    }
})();

DEBUG.log("banana", {foo:'bar'}); //[DEBUG 2:43:21 PM] banana Object {foo: "bar"}
console.log("Peppercorn");        //Peppercorn 
DEBUG.log("apple");               //[DEBUG 2:43:21 PM] apple 
DEBUG.log("orange");              //[DEBUG 2:43:21 PM] orange 
setTimeout(function(){
    DEBUG.log("mango");           //[DEBUG 2:43:25 PM] mango 
},3000)

This works because toString is called on timestamp (and, in fact, everything) each time console.log is called.

We overwrite the default toString method, and replace it with a time stamp (obviously you can change the output to whatever you want).

I chose the above pattern because, as others have noted (in SO chat), you can easily extend the DEBUG object to do other things.

...
return {
    log: console.log.bind(console, '%s', timestamp),
    error: console.error.bind(console, '%s', timestamp),
    info: console.info.bind(console, '%s', timestamp),
    warn: console.warn.bind(console, '%s', timestamp),
    group: ...,
    groupEnd: ...,
    groupCollapsed: ... // etc
}
...