Get the headers from a CSV file (and only that line)-CodePudding

How do I read the first non-empty line from a text file, in plain javascript, possibly by using a new FileReader()?

I wish to get only the first non-empty line, not the whole text in the file (which might be enormous). By "non-empty line" I mean a line ending with \r\n and containing some non-blank char.

One of my practical goals could be to pick the first "good" line in a huge CSV file, to possibly get the "headers" (names of variables of the dataset).

The file I wish to read is now locally on my hard disk, but when the script is ready, I would also like to put it online on my domain along with the script to process it.

Thank you!

CodePudding user response：

I think you want something kinda like this:

fs = require('fs')
fs.readFile('/testFile.csv', 'utf8', function (err,data) {
  if (err) {
    return console.log(err);
  }
    var firstLineRegEx = /^(.*)$/m
    var csvHeader = firstLineRegEx.exec(data)
});

CodePudding user response：

Assuming you want to stick to client-side/in-browser JavaScript (as opposed to node.js), there's not really a way to open a file and read it line-by-line; that would require a level of direct filesystem access that's simply not available. You can certainly process it line-by-line, once it's fully-loaded and you've split it into lines.

If you want to be sure that you only ever load the first line in the browser, you'll need some server-side code for that. Node.js may or may not be a good option, depending on your existing web site.

The FileReader API you mentioned looks like it's geared towards handling arbitrary, user-provided files, which is probably the wrong direction if you'll always be in control of what file to load.

You've actually got two, distinct problems here: how do I load only part of a file in client-side JS, and how can I find the header line in a string containing CSV formatted data? (You could probably break this down differently, but it's multiple parts regardless.)

CodePudding user response：

Do you absolutely have to useFileReader? and if so, does this help? How to read CSV headers and get them in to a list in java