CODEWITHSUNDEEP
javascriptcross-browsercross-platformecmascript-5console.log
Evan Carroll
Evan Carroll

Reputation: 1

How to best safely use console.log and console.warn?

I'm working to take over a code base that tests to make sure console.warn exists like this:

if (window.console) {                                                                                                                                                                                                                                                      
  console.warn("shhaabang");                                                                                                                                                                                                    
}

However, my problem with this is that it works only in the browser where you have a window object. This would seem to work too.

if (console && typeof console.warn == 'function') {                                                                                                                                                                                                                                                      
  console.warn("shhaabang");                                                                                                                                                                                                    
}

Are there any downsides to this method? Are there any better methods that don't assume the existence of window? Should I just see if window or global exists first and check both?

CLARIFICATION It should be obvious at the least that I'm testing this in something that doesn't have the window object. But, to be explicit I am running this in node.js as well as the browser

Upvotes: 5

Views: 2105

Answers (2)

Ryan Pfister
Ryan Pfister

Reputation: 138

Consider using a javascript logging framework that has already handed this rather than reinventing the wheel. For instance, try loglevel.

Here's how loglevel handles safe logging (view full source):

function realMethod(methodName) {
    if (typeof console === undefinedType) {
        return false; // We can't build a real method without a console to log to
    } else if (console[methodName] !== undefined) {
        return bindMethod(console, methodName);
    } else if (console.log !== undefined) {
        return bindMethod(console, 'log');
    } else {
        return noop;
    }
}

function bindMethod(obj, methodName) {
    var method = obj[methodName];
    if (typeof method.bind === 'function') {
        return method.bind(obj);
    } else {
        try {
            return Function.prototype.bind.call(method, obj);
        } catch (e) {
            // Missing bind shim or IE8 + Modernizr, fallback to wrapping
            return function() {
                return Function.prototype.apply.apply(method, [obj, arguments]);
            };
        }
    }
}

Upvotes: 2

mld
mld

Reputation: 36

you shouldn't do

if(console && typeof console.warn == "function"){ ... }

becuase this throws an error if console is not defined

you can use this

e.g.:

if(this.console){
  console.warn("shhaabang");
}

EDIT: oh sorry, i just noticed 2 things: 1) this does only work if this hasn't been changed... thanks @Evan Carroll 2) this does not work in strict mode, because in strict mode, this is undefined

so here's another approach:

var c;
try {
  c = console;
} catch(e){ 
  // console is not defined
}

if(c) {
  // console is defined
}else{
  // this will not throw because you declared `c` earlier
}

Upvotes: 0

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