This was a fun little build, but I wish I remembered to turn on my stream. It was kinda nice to just write some code, too πŸ˜‡

<LogViewer> takes a stream of server logs, or process logs, or any flat text file (let’s be honest) and turns it into a searchable, filterable little thing. Type in the input box, find what you’re looking for. Matched strings are highlighted so you know what you’re doing.

The whole thing fits into 69 lines of beautifully rendered code and 1071 node_modules dependencies. You can see the code on GitHub ✌️

Try <LogViewer>

Here’s how it works πŸ‘‡

<LogViewer> is built out of 2 main components:

  1. <LogViewer> renders a Downshift component and munches a text file into a list of logs
  2. <LogRow> takes care of individual lines and highlighting matched strings


We’re using getDerivedStateFromProps to take our logs, which is a flat string, and turn it into an array of entries. Right now, that’s just splitting by newlines, but we could perform contextual parsing and understand that a single log can span multiple lines.

Perhaps the parser function should come from props πŸ€”

The render method takes logs from state and returns a <Downshift> component. Downshift takes care of driving our input field and some other tidbits that are tedious to do ourselves.

Inside Downshift’s render prop, we use matchSorter to filter logs based on user input. I don’t know what string matching algorithm matchSorter uses, but it’s really fast.

A+ library πŸ‘Œ

Finally, we render a <div> with an input field controlled by Downshift, a p with the count of matches, and a pre with all our logs in a loop. We render each log entry with <LogRow>, providing the current match and log to be rendered.


The <LogRow> component renders a string of text, potentially highlighting a part of it.

We convert the matched string to lower case. Gonna use it to decide which part of the log to highlight.

Then we split our log on a regex using the provided match.

The result is an array of log fragments like this

match = 'cat'
log = 'my cat is grumpy'

chunks --> ['my ', 'cat', ' is grumpy']

When you split on regex and wrap your split point in parenthesis, (), it’s preserved in your output. Perfect πŸ‘Œ for our purposes and pretty fast too.

Rendering is a matter of looping through our chunks array and returning either a flat string or the <Highlighted> styled component.

The <Highlighted> component is simplistic because I’m no designer.

const Highlight = styled.span`
    color: red;
    background: yellow;

Red color, yellow background. High contrast.


That was an MVP. Should I make it better? Should I open source it?

Anyone out there who’d use it? 🀨 Ping me on Twitter.

Learned something new? Want to become a better engineer? πŸ’Œ

Join 9,400+ people just like you already improving their skills.

Here's how it works πŸ‘‡

Leave your email and I'll send you an Interactive Modern JavaScript Cheatsheet πŸ“– right away. After that you'll get a thoughtfully written email every week aboutΒ React, JavaScript,Β  andΒ lessons learned in my 20 years of writing code for companies ranging from tiny startups to Fortune5 behemoths.

Man, I love your way of writing these newsletters. Often very relatable and funny perspectives about the mundane struggles of a dev. Lightens up my day. ~ Kostas

PS: You should also follow me on twitter πŸ‘‰ here.
It's where I go to shoot the shit about programming.