Read a local text file constantly

Question

I'm a little lost on how I can read a local text file constantly. Nothing is going to a webserver, everything is done locally and its just something basic.

Essentially I have a text file that is getting updated constantly (A different program is writing to the text file), and I want to be able to read that text file. I just want to do something basic where a div gets auto updated with text file content without refreshing the page.

See [this thread](https://stackoverflow.com/questions/14446447/how-to-read-a-local-text-file) for canonical FS access from browser. — ggorlen, Dec 31 '20 at 19:30

score 4 · Accepted Answer · answered Dec 31 '20 at 10:22

Thanks to the File System Access API we can now keep live links to resources on the disk and request their content when we wish. (Previously, Files only kept a snapshot of a file on disk).

So in modern Chrome we can now request access to a file on disk using the window.showOpenFilePicker method.
This will return a list of handles, from which we will be able to call the getFile() method to get an up-to-date snapshot of the file on disk.

// must come from an user gesture
onclick = async () => {
  
  if( !("showOpenFilePicker" in self) ) {
    throw new Error( "unsupported browser" );
  }

  const handles = await showOpenFilePicker();
  
  setInterval( async () => {
    const file = await handles[0].getFile();
    document.getElementById( "log" ).textContent = await file.text();
  }, 1000 );
  
};

Since this API is over-protected, it can't run in cross-domain iframes, so here is an outsourced glitch demo, which currently works only in Chrome.

Interesting approach. Would there also be a possibility to directly access a local file without having to go through the file picker? — Carsten Massmann, Dec 31 '20 at 11:49
@cars10m That would be a massive security breach. What will then be stopping a malicious website from deleting your files without your intervention — Yossi Sternlicht, Dec 31 '20 at 11:54

Read a local text file constantly

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