compare texts horizontally

gistfile1.txt

const fs = require('fs')
let lineWidth = 0;
let betweenCharacters = 2;
let allTexts = [];

process.argv.forEach((val, index) => {
  //console.log(val);
  if(val.endsWith('.txt')){
    //console.log(val);
    try {
      const data = fs.readFileSync(val, 'utf8');
      let lines = data.split("\n"); 
      var longest = lines.sort(
          function (a, b) {
              return b.length - a.length;
          }
      )[0];
      
      allTexts.push({ data, startAt: 0, maxLineWidth: longest.length});      
    } catch (err) {
      console.error(err)
    }
  }
  else if(val == '-s')
  {
    lineWidth = Number(process.argv[index+1]);
  }
  else if(val == '-c')
  {
    betweenCharacters = Number(process.argv[index+1]);
  }
});


const isBelowThreshold = (currentValue) => currentValue.startAt >= currentValue.data.length;
let allLines = '';
while(true){ 

  if(allTexts.every(isBelowThreshold))  break;

  let oneLine = '';
  
  for(let i = 0; i < allTexts.length; i++){
    let t = allTexts[i];
    
    let ol = t.data.slice(t.startAt, t.startAt + (lineWidth == 0 ? t.maxLineWidth : lineWidth));
    let nIndex = ol.indexOf('\n'); 
    
    if(nIndex == 0 && t.data[t.startAt - 1] != '\n'){
      t.startAt += 1;
      i--;
      continue;
    }
    
    if(nIndex >= 0)
    {
      ol = ol.slice(0, nIndex) + ' '.repeat((lineWidth == 0 ? t.maxLineWidth : lineWidth) - nIndex);
      t.startAt += nIndex + 1;
    }
    else
    {
      t.startAt += ol.length;
      ol += ' '.repeat((lineWidth == 0 ? t.maxLineWidth : lineWidth) - ol.length);
    }
    
    if(i != allTexts.length -1)
      ol += ' '.repeat(betweenCharacters);
      
    oneLine += ol;
  };

  allLines += oneLine + '\n';
  
}

process.stdout.write(allLines);