Encode and decode urls.

url.ts

/**
 * RegExpURL matches URLs containing a query string.
 * - [0] full match
 * - [1] base url
 * - [2] query string
 * - [3] hash (without #)
 */
const RegExpURL = /^(.*)\?([^#]*)(?:#(.*))?$/
/**
 * RegExpListKey matches a URL key/value pair that uses array syntax (`key[]=value`).
 * - [0] full match
 * - [1] key
 * - [2] index
 * - [3] value
 */
const RegExpListKey = /^(.+)\[(\d*)]=(.+)$/

export function Decode(queryString: string) {
  let decoded: object = Object.create(null),
    matches: string[] | null = null,
    k = "",
    v = ""

  // Test for a full URL. If match, extract query.
  if (RegExpURL.test(queryString) && (matches = RegExpURL.exec(queryString)) != null) {
    queryString = matches[2]
    matches = null
  }

  for (const kvPair of queryString.split("&")) {
    // Test for list key items (`key[]=value`).
    if (RegExpListKey.test(kvPair) && (matches = RegExpListKey.exec(kvPair)) != null) {
      k = decodeURIComponent(matches[1])
      v = decodeURIComponent(matches[3])
      matches = null
      if (!Array.isArray(decoded[k])) {
        decoded[k] = []
      }
      decoded[k].push(v)
      continue
    }

    ;[k, v] = kvPair.split("=")
    if (!k) {
      continue
    }

    decoded[decodeURIComponent(k)] = decodeURIComponent(v)
  }

  return decoded
}

export function Encode(data: object) {
  let encoded = []

  for (const k of Object.getOwnPropertyNames(data)) {
    if (typeof data[k] == "function" || data[k] === undefined) {
      continue
    }

    if (Array.isArray(data[k])) {
      for (const v of data[k]) {
        encoded.push(encodeURIComponent(k) + "[]=" + encodeURIComponent(v))
      }
      continue
    }

    encoded.push(encodeURIComponent(k) + "=" + encodeURIComponent(data[k]))
  }

  return encoded.join("&")
}