JavaScript: Convert an array of objects to a comma-separated values string that contains only the columns specified

JavaScript fundamental (ES6 Syntax): Exercise-5 with Solution

Write a JavaScript program to convert an array of objects to a comma-separated value (CSV) string that contains only the columns specified.

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

Sample Solution:

JavaScript Code:

// Source: https://bit.ly/2neWfJ2

// Define a function called `JSON_to_CSV` that converts JSON data to CSV format.
const JSON_to_CSV = (arr, columns, delimiter = ',') =>
  [
    // Combine column titles with the delimiter.
    columns.join(delimiter),
    // Map each object in the array to a CSV row.
    ...arr.map(obj =>
      // For each object, reduce the values corresponding to the specified columns into a CSV row.
      columns.reduce(
        (acc, key) => `${acc}${!acc.length ? '' : delimiter}"${!obj[key] ? '' : obj[key]}"`, // Format value within double quotes.
        ''
      )
    )
  ].join('\n'); // Join rows with newline characters.

// Test cases
console.log(JSON_to_CSV([{ x: 100, y: 200 }, { x: 300, y: 400, z: 500 }, { x: 6 }, { y: 7 }], ['x', 'y']));
console.log(JSON_to_CSV([{ x: 100, y: 200 }, { x: 300, y: 400, z: 500 }, { x: 6 }, { y: 7 }], ['x', 'y'], ';'));

Sample Output:

x,y
"100","200"
"300","400"
"6",""
"","7"
x;y
"100";"200"
"300";"400"
"6";""
"";"7"

Flowchart:

Live Demo:

See the Pen javascript-basic-exercise-1-5 by w3resource (@w3resource) on CodePen.

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