format.ts

import { curryRight, flow, join } from "lodash";

import split from "./split";
import reverse from "./reverse";

/**
 * Thousand Regular Expression
 */
const thousandRegExp:RegExp = /[0-9]{1,3}/g;

/**
 * @example splitCurry(RegExp)(string)
 */
const splitCurry:Function = curryRight(split);

/**
 * @example joinCurry(separator)(string)
 */
const joinCurry:Function = curryRight(join);

export default function thousandSeparator(separator:string):Function {
    return flow([
        reverse,                    
        splitCurry(thousandRegExp),  
        joinCurry(separator),
        reverse,
    ]);
}