Pass arguments to console.log as first class arguments via proxy function

Question

console.log takes an unspecified number of arguments and dumps their content in a single line.

Is there a way I can write a function that passes arguments passed to it directly to console.log to maintain that behaviour? For example:

function log(){
    if(console){
        /* code here */
    }
}

This would not be the same as:

function log(){
    if(console){
        console.log(arguments);
    }
}

Since arguments is an array and console.log will dump the contents of that array. Nor will it be the same as:

function log(){
    if(console){
        for(i=0;i<arguments.length;console.log(arguments[i]),i++);
    }
}

Since that will print everything in different lines. The point is to maintain console.log's behaviour, but through a proxy function log.

+---

I was looking for a solution I could apply to all functions in the future (create a proxy for a function keeping the handling of arguments intact). If that can't be done however, I'll accept a console.log specific answer.

Gabriele Petrioli · Accepted Answer · 2017-12-13 16:28:22Z

98

This should do it ..

function log() {
    if(typeof(console) !== 'undefined') {
        console.log.apply(console, arguments);
    }
}

Just adding another option (using the spread operator and the rest parameters - although arguments could be used directly with the spread)

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

edited Dec 13, 2017 at 16:28

answered Oct 29, 2011 at 23:29

Gabriele Petrioli

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5 Comments

aditya Over a year ago

This doesn't work in Chrome/Safari. It throws an "Illegal invocation" error.

Gabriele Petrioli Over a year ago

@aditya, updated code.. i was not using the correct context.. you need to pass console as the this argument to apply..

purefusion Over a year ago

Just to point out, using this in your script will still cause errors in IE9 or older (or even IE10 if you're not using the <meta http-equiv="X-UA-Compatible" content="IE=edge" /> tag) breaking your script on your first call to log(); Instead of if(console) you should do if(typeof(console) !== 'undefined') which works in browsers new and old, including IE6-IE11.

jontro Over a year ago

Updated the answer to use typeof as @purefusion pointed out. There is no drawback

commonpike Over a year ago

missing a { before console.log.apply

nheinrich · Accepted Answer · 2011-10-29 23:33:53Z

There is a good example from the html5boilerplate code that wraps console.log in a similar way to make sure you don't disrupt any browsers that don't recognize it. It also adds a history and smoothes out any differences in the console.log implementation.

It was developed by Paul Irish and he has written up a post on it here.

I've pasted the relevant code below, here is a link to the file in the project: https://github.com/h5bp/html5-boilerplate/blob/master/js/plugins.js

// usage: log('inside coolFunc', this, arguments);
// paulirish.com/2009/log-a-lightweight-wrapper-for-consolelog/
window.log = function(){
  log.history = log.history || [];   // store logs to an array for reference
  log.history.push(arguments);
  if(this.console) {
    arguments.callee = arguments.callee.caller;
    var newarr = [].slice.call(arguments);
    (typeof console.log === 'object' ? log.apply.call(console.log, console, newarr) : console.log.apply(console, newarr));
  }
};

// make it safe to use console.log always
(function(b){function c(){}for(var d="assert,count,debug,dir,dirxml,error,exception,group,groupCollapsed,groupEnd,info,log,timeStamp,profile,profileEnd,time,timeEnd,trace,warn".split(","),a;a=d.pop();){b[a]=b[a]||c}}((function(){try {console.log();return window.console;}catch(err){return window.console={};}})());

Niet the Dark Absol · Accepted Answer · 2011-10-29 23:28:44Z

4

Yes.

console.log.apply(null,arguments);

Although, you may need to loop through the arguments object and create a regular array from it, but apart from that that's how you do it.

answered Oct 29, 2011 at 23:28

Niet the Dark Absol

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6 Comments

aditya Over a year ago

This doesn't work in Chrome/Safari. It works in Firebug, but looking for a cross-browser solution here.

Niet the Dark Absol Over a year ago

args = []; for(i=0; i<arguments.length; i++) args.push(arguments[i]); console.log.apply(null,args); - try that.

aditya Over a year ago

Nope. Apparently, any call to console.log.apply throws an Illegal invocation error.

Niet the Dark Absol Over a year ago

Okay, what if you try console.log(args.join('')); instead of console.log.apply in my last bit of code?

aditya Over a year ago

That wouldn't be what I want. If one does log({}), it'll say [object Object] and not the usual.

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