Will console.log reduce JavaScript execution performance?

Question

Will use of the debugging feature console.log reduce JavaScript execution performance? Will it affect the speed of script execution in production environments?

Answer 1

I do it this way to maintain original signature of console methods. In a common location, loaded before any other JS:

var DEBUG = false; // or true 

Then throughout code

if (DEBUG) console.log("message", obj, "etc");
if (DEBUG) console.warn("something is not right", obj, "etc");

Answer 2

If you create a shortcut to the console in a common core script, eg:

var con = console;

and then use con.log("message") or con.error("error message") throughout your code, on production you can simply rewire con in the core location to:

var con = {
    log: function() {},
    error: function() {},
    debug: function() {}
}

Answer 3

If you are going to have this on a public site or something, anyone with little knowledge on using the developer tools can read your debug messages. Depending on what you are logging, this may not be a desirable behavior.

One of the best approaches is to wrap the console.log in one of your methods, and where you can check for conditions and execute it. In a production build, you can avoid having these functions. This Stack Overflow question talks in details about how to do the same using the Closure compiler.

So, to answer your questions:

1. Yes, it will reduce the speed, though only negligibly.
2. But, don't use it as it's too easy for a person to read your logs.
3. The answers to this question may give you hints on how to remove them from production.

Answer 4

const DEBUG = true / false
DEBUG && console.log('string')

Answer 5

Any function call will slightly reduce performance. But a few console.log's should not have any noticeable effect.

However it will throw undefined errors in older browsers that don't support console

Answer 6

I made this jsPerf test: http://jsperf.com/console-log1337

It doesn't seem to take any longer than other function calls.

What about browsers that doesn't have a console API? If you need to use console.log for debugging, you might include a script in your production deployment to override the console API, like Paul suggests in his answer.