How can I determine in JS if a function/method exists in IE7?

Question

I wrote a quick and dirty logger as a jQuery plugin

(function($){   
    $.log = function(debug) {  
     if (console.debug) {   
      console.debug(debug);   
     };  
    };
})(jQuery);

It works fine in Firefox, but in IE7, I'm getting the error

console.debug is null or not an object

How do I perform a function exists in JavaScript that's compatible with IE7?

Thanks

Answer 1

console.debug is specific to Firebug, which runs under Firefox.

You need to check if window.console is available before checking for console.log!

Here's your code reworked with no errors:

(function($){
    $.log = function(debug) {
     if (window.console && console.debug) {
       console.debug(debug);
     };
    };
})(jQuery);

Answer 2

Check if console is defined, then check if debug is a function:

if (typeof(console) != 'undefined' && typeof(console.debug) == 'function'){
  //...
}

Answer 3

$.log = window.console && console.debug ? function(debug) { console.debug(debug); } : function(){};

Variations:

$.log = function( debug ) {
    if ( window.console && console.debug ) { 
        console.debug( debug )
    }
}

$.log = function( msg ) {
    if ( window.console ) {
       if ( console.debug ) console.debug ( msg ) 
       else if ( console.log ) console.log ( msg )
    }
}

$.log = function( msg ) {
    if ( typeof console === 'object' && typeof console.debug === 'function' ) { 
       console.debug( msg )
    }
}

$.log = 'console' in window && console.debug ? function(m){console.debug(m)}:function(){}

$.log = function() {
     if ( 'console' in window ) {
         console.debug ? function(m){console.debug(m)} : ( console.log ? function(m){console.log(m)} : function(){}
     }
}

$.log = window.log = function(m){ if(window.console && console.debug) console.debug(m) }

Answer 4

The above answers are all correct, but you're going to have the side effect of your log statements being converted from an arguments object into an array, and your output will look (something) like this:

["my", "debug", "statement"]

To fix that you need to forward the arguments object and keep it intact:

$.log = function() { // note no arguments used
    if ( window.console && console.debug ) { 
        console.debug.apply(console, arguments )
    }
}

Now the output will look like:

My debug statement