`formatUrl` function that formats query params and such

format-url.js

import * as _ from 'lodash';

let n = 2;
let someString;

// NOTE `_.pickBy(params, _.negate(_.isNil))` removes undefined/null entries
// so you don't have to worry about `undefined` getting coerced to a string
const formatUrl = (urlStr, params) => urlStr + '?' + 
      new URLSearchParams(_.pickBy(params, _.negate(_.isNil))).toString();

fetch(formatUrl('/endpoint', {
  foo: n > 1 ? 123 : 456,
  bar: '1%', // this gets encoded automatically
  query: someString // this entry gets removed because it's undefined
}));

// the formatted URL is "/endpoint?foo=123&bar=1%25"