line-file-reader

Modern line-by-line File reader

Easily read File or Blob objects line by line.

Getting started

Install it using NPM.

npm i line-file-reader

You can also find a JS file that you can copy and use in <script> tags in stub/browser.js.

Usage

You can simply use it with the ES2018 async iterator.

Please be warned that line separator (default: \n) will not be returned in iterated lines. To customize line separator, see Customize iteration part.

Simple usage

import LineFileReader from 'line-file-reader';

const file = new File(["Some\nlines\n...\n"], "content.txt");
const reader = new LineFileReader(file);

for await (const line of reader) {
  console.log(line);
}

Multiple iteration

You can iterate multiple times, and concurrently on the same file.

for await (const line of reader) {
  // Do something with line..
  // Read the file during file read

  for await (const line_second of reader) {
    // do this action is safe!
  }
}

Customize iteration

By default, iteration is made with the \n separator (UNIX new lines), using chunks of 1024 bytes.

You can customize those settings by using the .iterate() method (Symbol.asyncIterator is just an alias of .iterate without arguments).

const reader = new LineFileReader(file);

const async_iterator = reader.iterate(
  // Here, you can use string, even of multiple characters.
  /* separator = */ '\n',

  // This is only a parameter to adjust for performance sake (in bytes).
  // Higher length = higher performance = higher RAM consumption
  /* chunk_length = */ 1024
);

for await (const line of async_iterator) {
  // Do sth with line...
}