[NodeJS] CSV data transform example using stream

csv-transform-example.js

// Define the transform rule
const transformRules = [
  upperCase, // col idx 0: To uppercase. ``upperCase` is function.
  { "1":"1st", "2":"2nd", "3":"3rd" }, // col idx 1: 1=>"1st", 2=>"2nd", ...
  { "A":"PlanA", "B":"PlanB", "C":"PlanC" },// col idx 2: "A"=>"PlanA", ...
];

const fs = require("fs");
const readStream = fs.createReadStream(__dirname + "/input.csv" );
const writeStream = fs.createWriteStream(__dirname + "/output.csv", { encoding: "utf8" } );

const lineReader = require('readline').createInterface({
  input: readStream,
  output: writeStream,
});
lineReader.on('line', function (line) {
  const cols = line.split(",");
  const newCols = transform(cols, transformRules);
  console.log(cols, "=>", newCols);
  writeStream.write(newCols.join(",") + "\n");
});
lineReader.on('close', function() {
  console.log("close");
  process.exit(0);
});

function transform(cols, rules){
  const newCols = [];
  for (let len = cols.length, i = 0; i < len; i++){
    const col = cols[i];
    const rule = rules[i];
    if (!rule) {
      newCols[i] = col;
      continue;
    }
    if (typeof rule === "function"){
      newCols[i] = rule(col);
      continue;
    }
    newCols[i] = rule[col];
  }
  return newCols;
}

function upperCase(s) {
  if (!s) return s;
  return s.toUpperCase();
}

input.csv