Convert JSON data to CSV data.

json-to-csv.ts

/*
 * Created by Trevor Sears <[email protected]> (https://trevorsears.com/).
 * 12:43 PM -- September 14th, 2021
 */
 
/**
 * Returns all of the unique properties found in any of the objects within the given array.
 * 
 * @param {T[]} jsonArray The array of objects over which to build a list of unique properties.
 * @returns {Array<keyof T>} An array containing all of the unique properties found in any of the objects within the
 * given array.
 */
function getAllUniqueProps<T>(jsonArray: T[]): Array<keyof T> {
	
	let props: Set<keyof T> = new Set();
	
	for (let json of jsonArray) {
		
		for (let prop of Object.getOwnPropertyNames(json)) {
			
			props.add(prop as keyof T);
			
		}
		
	}
	
	return [...props];
	
}

/**
 * Returns a 'cleaned' string representation of the input value.
 * 
 * This is the default 'cleaner' function used to sanitize/clean CSV data for the `jsonToCSV` function.
 * 
 * @param {any} value The value to 'clean'.
 * @param {string} separator The separator string being used in the relevant CSV data.
 * @returns {string} A 'cleaned' version of the input value.
 */
function cleanCSVData(value: any, separator: string): string {
	
	if (value === true) return "1";
	else if (value === false) return "0";
	
	if (typeof value === "string" && value.includes(separator)) return `"${value}"`;
	
	return value;
	
}

/**
 * Converts a JSON array to a CSV-style string, returning the result.
 *
 * @param {T[]} jsonArray The array of objects from which to source the data for the CSV string result.
 * @param {Array<keyof T>} fields An optional array of strings that will be used as the fields of the resulting CSV.
 * @param {string} separator The string to use to separate cells in the resulting data.
 * @param {(value: string) => string} cleaner An optional callback that will be applied to every value (cell) before
 * being used in the output string.
 * @returns {string} A string representation of the generated CSV data.
 */
export function jsonToCSV<T>(jsonArray: T[],
							 fields: Array<keyof T> = getAllUniqueProps(jsonArray),
							 separator: string = ",",
							 cleaner: (value: any, separator: string) => string = cleanCSVData): string {
	
	let result: string = "";
	
	result += fields.join(separator);
	
	for (let json of jsonArray) {
		
		let values: string[] = fields.map((property: keyof T): string => cleaner(json[property], separator));
		
		result += `\n${values.join(separator)}`;
		
	}
	
	return result;
	
}

// Example usage:

console.log(jsonToCSV([
	{
		id: 1,
		name: "John"
	},
	{
		id: 2,
		name: "Jess"
	},
	{
		id: 3,
		name: "Junior"
	}
]));

/* id,name
 * 1,John
 * 2,Jess
 * 3,Junior
 */

console.log(jsonToCSV([
	{
		id: 1,
		name: "John",
		email: "[email protected]"
	},
	{
		id: 2,
		name: "Jess",
		phone: "(123) 456 - 7890"
	},
	{
		id: 3,
		name: "Junior",
		fax: "no one uses fax anymore"
	}
], undefined, "|"));

/* id|name|email|phone|fax
 * 1|John|[email protected]||
 * 2|Jess||(123) 456 - 7890|
 * 3|Junior|||no one uses fax anymore
 */

console.log(jsonToCSV([
	{
		id: 1,
		name: "John"
	},
	{
		id: 2,
		name: "Jess"
	},
	{
		id: 3,
		name: "Junior"
	}
], ["fields", "that", "don't", "exist"]));

/* fields,that,don't,exist
 * ,,,
 * ,,,
 * ,,,
 */