node.jsfast-csv

Node.js fast-csv synchronously read file and return array


I am trying to read a .csv file and to assign it to an array with this code:

const fs = require("fs");
const csv = require("@fast-csv/parse");

let data = []

csv
  .parseFile("./downloads/aggiornamento.csv", { skipRows: 2 })
  .on("error", (error) => console.error(error))
  .on("data", (row) => {
    let obj = {};
    obj["item_id"] = row[2];
    obj["qty"] = row[20];

    data.push(obj);
    console.log(obj);
  })
  .on("end", function () {
    return data;
  });

However, the file read by fast-csv is a stream, hence I can only process row by row. I need the full array in a second moment to call some API service, hence I would like to read the file synchronously, appending very row, and returning the array at the end, so that, in a second moment, I can wrap the previous code in a function, and obtain the array in a way such as:

const data = readCSVSynchronously()

How can I do it with fast-csv?


Solution

  • You can't turn an asynchronous function into a synchronous one.

    You could, however, wrap that eventful reading code into a promise, which you can then use in a promise/async context, like so:

    const fs = require("fs");
    const csv = require("@fast-csv/parse");
    
    function readCsv(path, options, rowProcessor) {
      return new Promise((resolve, reject) => {
        const data = [];
    
        csv
          .parseFile(path, options)
          .on("error", reject)
          .on("data", (row) => {
            const obj = rowProcessor(row);
            if (obj) data.push(obj);
          })
          .on("end", () => {
            resolve(data);
          });
      });
    }
    
    async function doThings() {
      const data = await readCsv(
        "./downloads/aggiornamento.csv",
        { skipRows: 2 },
        (row) => ({ item_id: row[2], qty: row[20] }),
      );
      // use data in API...
    }