Format URL function that can be partially applied made for fun!

format_url.js

'use strict';

const qs = require('qs');

function format_url(base) {
  const remove_trailing_slash = (element) => {
    return element.endsWith('/') ? element.slice(1, -1) : element;
  };

  const remove_leading_slash = (element) => {
    return element.startsWith('/') ? element.slice(1) : element;
  };

  const append_element = (current_base) => {
    return (element) => {
      if (!element) {
        return current_base;
      }

      if (typeof(element) === 'object') {
        return current_base + '?' + qs.stringify(element);
      }

      return append_element(remove_trailing_slash(current_base) + '/' + remove_leading_slash(element));
    };
  };

  return append_element(base);
}

const base_url = format_url('https://example.com');

base_url('users')({ 'type': 'admin' }); // => https://example.com/users?type=admin
base_url('users')('1')('posts')(); // => https://example.com/users/1/posts