Schema based query string parser

urlQueryParamParser.js

const assert = require("assert");

const objectify = (o, [k, v]) => ({ ...o, [k]: v });

function parseFromURL(schema, url = window.location.search) {
  const searchParams = new URLSearchParams(url);

  return Object.entries(schema)
    .map(([par, { def }]) => [par, searchParams.get(par) ?? def ?? undefined])
    .map(([par, val]) => [par, schema[par].transform?.(val) ?? val])
    .reduce(objectify, {});
}

// a=1&b=null&c=undefined&d=&e=test
const url = new URLSearchParams({
  a: 1,
  b: null,
  c: undefined,
  d: "",
  e: "test",
  f: JSON.stringify({ name: "test" }),
}).toString();

const schema = {
  a: {
    def: 5,
    transform: String,
  },
  b: {},
  c: {},
  d: {
    def: "undefined",
    transform: Boolean,
  },
  f: {
    def: {
      name: "test",
    },
    transform: JSON.parse,
  },
};

const { a, b, c, d, e, f, g, h } = parseFromURL(schema, url);

assert(a === "1");
assert(b === "null");
assert(c === "undefined");
assert(d === false);
assert(e === undefined);
assert(f.name === "test");