In my React webapp, how do I show the right date in a "Website last updated" field? - node.js

Question

I'm putting together a demo app in which I frequently add content and new React components. I have just added the component react-timeago for showing when the latest changes were made to the site. Now I want to give that component the right timestamp.
At worst, I suppose I could show the last time that the server was started. I am using webpack-dev-server locally. I haven't yet gone live with this site, but it will probably (like webpack-dev-server) be an express-based solution when I do. So one option is perhaps to do a grep on an express-generated logfile for server start entries. Solving that would solve the question to an extent. It's worth noting though that adding content would not require a restart, so this solution is perhaps not ideal. Presumably, I could use some kind of middleware (logger or otherwise) in express for this.
Another possible approach might be some kind of directory watch mechanism that records the last time a change was made. Should I somehow hook this into a redux state, for example? There are so many components available that it's difficult to know which ones to put together (with my limited experience in this area) to achieve this.
My site is a lightweight single pager and I'm loath to add any kind of datastore behind it at this stage as it seems like overkill to me.
I can also mention that I'm using webpack 2. Aside from that it's a really basic React app with a couple of components.
To summarize, I am after some way of looking for added content (eg. mp3 files) or changed code files, and getting that timestamp into my react-timeago component.

Answer 1

As #Joe Clay suggested, I used Webpack.DefinePlugin to fill a constant with the current time at restart. This worked fine, I added the following lines into my webpack.config.js:
var dateString = new Date().toDateString();
...
new webpack.DefinePlugin({
LAST_UPDATED: JSON.stringify(dateString)
})
And was able to access the the constant in my React component:
<div style={{marginTop:120}}>A sinewave440hz demo site.<br/>
This site was updated
<TimeAgo date={LAST_UPDATED} formatter={formatter}/>.
</div>
Recording changes in the assets could also be done at startup if the previous state of the assets was recorded somewhere.