JavaScript - how to build build an hierarchy object from a CSV file

First, the "better" of the two answers.

You'll see it follows mostly the same flow as you started with, however, I chose to put all the parsing up front, into some intermediate objects. This allows the latter code to focus on just building our tree.

let csv = `id, category, year, color, price \n
01, SUV > AWD > Sport > Benz, 2017, blue, $20 \n
02, SUV > FWD > Family > Benz, 2018, black, $20 \n
03, Sedan > AWD > BNW, 2017, white, $30 \n
04, SUV > AWD > Sport > BNW, 2012, red, $30 \n
05, Sedan > RWD > Toyota, 2019, white, $30`;

function parseCsv(csv) {
  let object = {};

  // Parse/Sanitize all the data up front
  const rows = csv
    .split("\n")
    .filter((row, index) => index && row)
    .map((row) => {
      const columns = row.split(",");
      return {
        headers: columns[1].split(">").map((p) => p.trim()),
        color: columns[3].trim()
      };
    });

  // Then spin through the rows
  for (const row of rows) {
    let currentObj = object;

    // Then spin through the headers
    for (let hi = 0; hi < row.headers.length; ++hi) {
      const header = row.headers[hi];

      // If it is the last header, assign the color to it
      if (hi === row.headers.length - 1) {
        currentObj[header] = row.color;
        break;
      }

      // Else we need to get or set another object level
      currentObj = currentObj[header] = currentObj[header] ?? {};
    }
  }

  return object;
}

console.log(parseCsv(csv));

Second, I took another approach here. I find some elegance in a recursive solution. Although, it is probably harder to read, will most likely utilize more memory, and be slower, especially has the document/header depth grows. But I included it for fun!

let csv = `id, category, year, color, price \n
01, SUV > AWD > Sport > Benz, 2017, blue, $20 \n
02, SUV > FWD > Family > Benz, 2018, black, $20 \n
03, Sedan > AWD > BNW, 2017, white, $30 \n
04, SUV > AWD > Sport > BNW, 2012, red, $30 \n
05, Sedan > RWD > Toyota, 2019, white, $30`;

const parseCsv = (csv) => {
  const result = {};

  // Parse/Sanitize all the data up front
  const rows = csv
    .split("\n")
    .filter((row, index) => index && row)
    .map((row) => {
      const columns = row.split(",");
      return {
        headers: columns[1].split('>').map(p => p.trim()),
        color: columns[3].trim()
      };
    });

  // The recursive function, takes in
  // {target} the current object in the tree we're  at
  // {headers} the remaining headers to step through
  // {color} the color to assign to the last header
  const handleRow = (target, headers, color) => {
    // Last header, so just assign the color to it
    if (headers.length === 1) {
      target[headers[0]] = color;
      return;
    }

    // Else we need to get or set another object level
    const newTarget = (target[headers[0]] = target[headers[0]] ?? {});
    // And call into the next level with it and the remaining headers
    handleRow(newTarget, headers.slice(1), color);
  };

  for (const row of rows) {
    handleRow(result, row.headers, row.color);
  }

  return result;
};

console.log(parseCsv(csv));