Testing for console.log statements in IE [duplicat

Question

Possible Duplicate:
'console' is undefined error for internet explorer

If you have console.log statements in your code, Internet Explorer will throw a JavaScript error (at least in IE7 which is what our intranet users have installed).

I am using Firefox for most of my development testing primarily because of the functionality provided by Firebug (where I use a lot of console statements) but I also need to test in IE.

if I add the following to my JavaScript, the error does not get thrown.

var debugging = false;
if (typeof console == "undefined") 
    var console = { log: function() {} };  

The problem is that I would like to trigger an event if debugging mode is false. If I create a function to test whether debugging is false and do an action (at this point just an alert) but when I try do the following I receive an IE error saying Console is not defined.

var debugging = false; // or true   
if (typeof console == "undefined") 
    var console = { log: function() {consoleMsg()} };   

function consoleMsg() {
    if(!debugging) {
    alert('Console.log event in Production Code');
}   

If someone could help me to fix my code, provide a better way to help me achieve my goal, or direct me to a resource to edumacate myself I would be very appreciative.

Answer 1

'console' itself needs to be a function, as well as 'log'. So:

if(typeof(console) === 'undefined') {
    console = function(){};
    console.log = function(){consoleMsg()};
}   

Answer 2

You don't have to jump through all these hoops. Simply check if the console exists before using it.

So, instead of:

console.log('foo');

Use:

window.console && console.log('foo');

...and you won't get any errors.

---

Alternatively, you could just check for it at the top of your script, and if it's undefined, just fill it with an empty function:

// At the top of your script:
if ( ! window.console ) console = { log: function(){} };
// If you use other console methods, add them to the object literal above

// Then, anywhere in your script:
console.log('This message will be logged, but will not cause an error in IE7');

---

For a more robust solution, use this piece of code (taken from twitter's source code):

// Avoid `console` errors in browsers that lack a console.
(function() {
    var method;
    var noop = function () {};
    var methods = [
        'assert', 'clear', 'count', 'debug', 'dir', 'dirxml', 'error',
        'exception', 'group', 'groupCollapsed', 'groupEnd', 'info', 'log',
        'markTimeline', 'profile', 'profileEnd', 'table', 'time', 'timeEnd',
        'timeStamp', 'trace', 'warn'
    ];
    var length = methods.length;
    var console = (window.console = window.console || {});

    while (length--) {
        method = methods[length];

        // Only stub undefined methods.
        if (!console[method]) {
            console[method] = noop;
        }
    }
}());

Answer 3

(function(debug) {
    var console;

    function wrapConsoleMethod(fnName) {
        if(fnName in console)
            console[ fnName ] = function(fn) {
                return function() {
                    if(debug)
                        return fn.apply(console, arguments);
                    else
                        alert('Console event in Production Code');
                };
            }(console[ fnName ]);
        else
            ; // fn not in console
    };

    if(!('console' in window))
        window.console = {
            log : function() {}
            // ...
        };
    console = window.console;
    wrapConsoleMethod('log');
    // ...
})(true /* debug */);

console.log('test');

Answer 4

Did you try try-catch:

var debugging = false; // or true 
try {  
    console.log();
} catch(ex) {
    /*var*/ console = { log: function() {consoleMsg()} };   
}