4_1.js

const fileName = process.argv.slice(2)[0] || 'input.txt';

async function solve() {
  const lineReader = require('readline').createInterface({
    input: require('fs').createReadStream(fileName)
  });

  let containedCount = 0;

  for await (const line of lineReader) {
    const pair = line.split(',').map(rangeString => {
      const rangeSplit = rangeString.split('-');
      return {
        start: Number(rangeSplit[0]), 
        end: Number(rangeSplit[1])
      };
    });

    const former = pair[0];
    const latter = pair[1];
    // if first range is larger or equal to second or second range is larger or equal to first
    if ((former.start <= latter.start && former.end >= latter.end)
        || (former.start >= latter.start && former.end <= latter.end)) {
      containedCount++;
    }
  }
  console.log(containedCount);
}
  
solve();