JSON to CSV

JavaScript, Array, String, Object · Oct 13, 2021

Converts an array of objects to a comma-separated values (CSV) string that contains only the columns specified.

Use Array.prototype.join() to combine all the names in columns to create the first row, using the provided delimiter.
Use Array.prototype.map() and Array.prototype.reduce() to create a row for each object. Substitute non-existent values with empty strings and only mapping values in columns.
Use Array.prototype.join() to combine all rows into a string, separating each row with a newline (\n).
Omit the third argument, delimiter, to use a default delimiter of ','.

const JSONtoCSV = (arr, columns, delimiter = ',') =>
  [
    columns.join(delimiter),
    ...arr.map(obj =>
      columns.reduce(
        (acc, key) =>
          `${acc}${!acc.length ? '' : delimiter}"${!obj[key] ? '' : obj[key]}"`,
        ''
      )
    ),
  ].join('\n');

JSONtoCSV(
  [{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }],
  ['a', 'b']
); // 'a,b\n"1","2"\n"3","4"\n"6",""\n"","7"'
JSONtoCSV(
  [{ a: 1, b: 2 }, { a: 3, b: 4, c: 5 }, { a: 6 }, { b: 7 }],
  ['a', 'b'],
  ';'
); // 'a;b\n"1";"2"\n"3";"4"\n"6";""\n"";"7"'

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