Javascript - Adding a new column in an array using for loop - error

Question

I'm using an API to retrieve data on some stocks and I would like to add a column named symbol with the query values using the functon insertColumn but I'm getting an error (node:15732) UnhandledPromiseRejectionWarning: TypeError: Cannot read property 'result' of undefined. I've tried changing let result to this.result and then do insertColumn.call(this), but the same error occurs. I thought it would be related with a closure error, but at this point I'm not sure

import ObjectsToCsv from 'objects-to-csv';
import yahooFinance from 'yahoo-finance2';



async function api(){

  const query = 'TSLA';
  const queryOptions = { period1: '2021-08-06', interval: "1d"};
  let result = await yahooFinance.historical(query, queryOptions);

    function insertColumn() {
      for (var i = 0; i < this.result.length; i++) {
        this.result[i].push({symbol: query});
      }
    };
    insertColumn();

  console.log(result);

  (async () => {
    const csv = new ObjectsToCsv(result);
    await csv.toDisk('C:/Users/Rafael Oliveira/Desktop/teste/test.csv');
  })();
};
api();

The output goes something like this:

[
  {
    date: 2021-08-06T00:00:00.000Z,
    open: 711.900024,
    high: 716.330017,
    low: 697.630005,
    close: 699.099976,
    adjClose: 699.099976,
    volume: 15576200
  },...

and I want it to be this:

[
  {
    date: 2021-08-06T00:00:00.000Z,
    open: 711.900024,
    high: 716.330017,
    low: 697.630005,
    close: 699.099976,
    adjClose: 699.099976,
    volume: 15576200
    symbol: 'TSLA' //this would be changed once I change the query part as well
  },

change ALL this.result to result .. and why is insertColumn a function, remove the function, keep the code inside it - similarly with your (async () => { ... remove that IIFE, kep its content - also, result[i].push({symbol: query}); doesn't look right, since result[i] is an object not an array — Bravo
– Bravo, Commented Aug 11, 2021 at 14:58

nomadoda · Accepted Answer · 2021-08-11 14:58:34Z

2

You should probably rather use javascript Array.prototype.map and append symbol to each item:

import ObjectsToCsv from 'objects-to-csv';
import yahooFinance from 'yahoo-finance2';

async function api(){
  const query = 'TSLA';
  const queryOptions = { period1: '2021-08-06', interval: "1d" };
  const result = await yahooFinance.historical(query, queryOptions);
  const resultWithSymbol = result.map((item) => ({ ...item, symbol: query }));

  console.log(resultWithSymbol);

  (async () => {
    const csv = new ObjectsToCsv(resultWithSymbol);
    await csv.toDisk('C:/Users/Rafael Oliveira/Desktop/teste/test.csv');
  })();
};
api();

answered Aug 11, 2021 at 14:58

nomadoda

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3 Comments

Bravo Over a year ago

I'd love to know the reasoning behind the async IIFE inside an async function

nomadoda Over a year ago

Yes, that is unnecessary

Bravo Over a year ago

Perhaps not, I can think of a reason it may be there - but not in this case, since nothing after the only await - i.e. you want to do some async/await that calling function doesn't need to wait for

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