How can I cache a csv for Papa Parse to parse?

Question

I am very unfamiliar with how caching works, and so I was wondering how I could pull a csv off a server the first time, but on subsequent refreshes use a cached csv file?

I know how to get the file from the server, and parse it via PapaParse. However, I do not know how to make that csv cached, or even how to access the cache via PapaParse.

Going further with this, how could I then check how long ago this csv file has been updated, and if it needs to be updated pull the csv off the server again? I understand there is a lastModified property in Javascript but it is unclear whether or not that works for cached files.

Answer 1

The browser and server you're downloading the CSV file from should negotiate caching for you; I might misunderstand but I'm not sure what Papa Parse would have to do with that.

For last modified date, if the file happens to be selected by the user with a <input type="file"> element on the page, you can access the File object and check its lastModified or lastModifiedDate properties (at least, they exist on Chrome).

To get the last modified date of a file to be downloaded, MDN has an example all ready for you:

function getHeaderTime () {
  alert(this.getResponseHeader("Last-Modified"));  /* A valid GMTString date or null */
}

var oReq = new XMLHttpRequest();
oReq.open("HEAD" /* use HEAD if you only need the headers! */, "yourpage.html", true);
oReq.onload = getHeaderTime;
oReq.send();

This simply does a HEAD request (to only check the last-modified and not get the whole file, all you need is the headers) and reads the Last-Modified header.