Run cell only once / Static timestamp

Community Help
1

Hi folks,

After some quick search I guess this might be one necessity in the notebooks. I wanted to create one static timestamp in my markdown part however the new Date() syntax will update every time the notebook get reloaded, and I wonder there’s one tricky way to have a static timestamp.
It also means that let certain cell only run once and suppress updating the cell even though the notebook get reloaded.
I’ve tried once = require('https://bundle.run/once@1.4.0') but I didn’t manage to get it work, also there’s a jquery one method but unfortunately I have no clue how to use it in markdown tagged literals.
Thanks for any sort of input you could provide!

2

I think you’d need to manually input the timestamp, as Observable will always run all the cells when the notebook is reloaded.

3

Thank you so much, it didn’t come to my mind such an easy trick!

4

You want a timestamp from the first time each user visits your notebook, which then persists when they reload?

You could try storing the timestamp in browser localStorage.

5

Good idea, then I tried this:


but when I reload the page the localStorage'd item got updated again, any idea how to fix it?

6

Oh, I get it, the trick is to claim an object that stores the information.

7

Oh, the timestamp is still updating itself every time I reload the page…

8

Here, https://observablehq.com/d/64ec69400e7f6224

timestamp = new Date(
  +localStorage.timestamp ||
  +(localStorage.timestamp = +new Date))

I’m just using localStorage as if it’s a regular object; you might prefer to use the getItem / setItem methods, along the lines of:

timestamp = new Date(
  +localStorage.getItem('timestamp') ||
  +(localStorage.setItem('timestamp', +new Date), localStorage.getItem('timestamp')))
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