index.ts

type KeyValue = string[]
type Result = Record<string, string | number | boolean>

const booleanDict = {
  true: true,
  false: false,
}

const nonValues = {
  undefined: true,
  null: true,
  empty: true,
  "n/a": true,
  // etc
}

const querystring = "to=kaluga&stars=3&free_wifi=true&from="

function clear(querystring: string): KeyValue[] {
  return querystring.split("&").map((el: string) => el.split("="))
}

function getValue(val: string): string | number | boolean {
  let value: string | number | boolean = val

  if (Object.prototype.hasOwnProperty.call(booleanDict, value)) {
    value = booleanDict[value]
  } else if (!isNaN(Number(value))) {
    value = Number(value)
  }

  return value
}

function parseQuery(querystring: string): Result {
  if (!querystring) return {}

  const parsedValues = clear(querystring)

  const result = parsedValues.reduce((acc, el) => {
    const [key, val] = el
    if (!val || nonValues[val.toLowerCase()]) return acc

    acc[key] = getValue(val)
    return acc
  }, {} as Result)

  return result
}

const parsedQueryString = parseQuery(querystring)

console.log(parsedQueryString)