json-to-csv.js

function squareImages({ width = 1, height = width } = {}) {
  return width / height === 1;
}

function collectionToCSV(keys = []) {
  return (collection = []) => {
    const headers = keys.map(key => `"${key}"`).join(',');
    const extractKeyValues = record => keys.map(key => `"${record[key]}"`).join(',');

    return collection.reduce((csv, record) => {
      return (`${csv}\n${extractKeyValues(record)}`).trim();
    }, headers);
  }
}

const exportFields = [ 'id', 'author', 'filename', 'format', 'width', 'height' ];

fetch('https://picsum.photos/list')
  .then(response => response.json())
  .then(data => data.filter(squareImages))
  .then(collectionToCSV(exportFields))
  .then(console.log, console.error);