Synchronously read a file line by line with NodeJS

getFileLinesSync.js

let fs = require('fs');
let string_decoder = require('string_decoder');

// Synchronously read the content of a text file one line at a time
// Note, caller must complete the iteration for file to be closed
//        ie: don't break out early from the loop calling this function
function* getFileLinesSync(filename, encoding)
{
    let fd = fs.openSync(filename);
    let buf = Buffer.allocUnsafe(32768);
    let pos = 0;
    let decoder = new string_decoder.StringDecoder(encoding || 'UTF8');
    let lineStart = "";

    while (true)
    {
        // Read buffer
        let bytesRead = fs.readSync(fd, buf, 0, buf.length, pos);
        pos += bytesRead;

        // Decode string
        let str;
        if (bytesRead < buf.length)
            str = lineStart + decoder.end(buf.subarray(0, bytesRead));
        else
            str = lineStart + decoder.write(buf);

        // Split into lines and yield the complete ones
        let lines = str.split(/\r?\n/);
        for (let i=0; i<lines.length - 1; i++)
        {
            yield lines[i];
        }

        // The last line is the start of the first line in the next chunk
        lineStart = lines[lines.length - 1];

        // quit if eof
        if (bytesRead < buf.length)
            break;
    }

    // Final line
    yield lineStart;
        
    fs.closeSync(fd);
}

module.exports = {
    getFileLinesSync,
}