The Radar Gun Problem

When `console.log` goes wrong

This post is still in the early stages. Beware - here be mental dragons!

The other day, I was driving home from an event and there was a massive slowdown
on the highway. I assumed that there was a crash or some construction up ahead,
but as I got closer to the bottleneck, I realized that the only difference was
that there was a cop standing on the side of the highway with a radar gun. Just
the presence of a monitor slowed down the performance of the system.

Later that week, I was debugging some Javascript code and ran into a problem I
have hit a few times. I had a fairly intensive process looping over a lot of
values. I took the standard approach to debug a JS problem and dropped in a
console.log. I refreshed the page, opened the console… and almost crashed my

Calling a console.log with an intensive process takes a lot of memory, it
turns out. I’ve run into this before, but this time the traffic slowdown really
made me think about it. Let’s talk a bit about something I’m calling the Radar
Gun Problem.

In many situations, the fix for the problem is changing where the observation
happens. Moving the console.log outside of the loop - either after or before -
is a good option. You can also change the method of observation - drop in a
debugger; and step through it, introducing a purposeful bottleneck to prevent
an accidental one.

Have you run into this before? How have you solved it?