Javascript (very incomplete) port of the "unserialize" PHP function

unserializePhp.js

function unserialize(serialized) {
  serialized = serialized.split("")
  const res = []

  const parseNumber = () => {
    next = serialized.shift()
    let digits = ""
    while (!isNaN(parseInt(next))) {
      digits += next
      next = serialized.shift()
    }
    return { value: parseInt(digits), next }
  }

  const parseString = (len) => {
    serialized.shift() // remove quote
    const str = serialized.splice(0, len)
    serialized.shift() // remove quote
    return { value: str.join(""), next: serialized.shift() }
  }

  const parseBool = () => {
    const value = serialized.shift()
    const next = serialized.shift()
    return { value, next }
  }

  const parse = (obj = [], parents = []) => {
    if (serialized.length === 0) return obj
    const type = serialized.shift()
    let parsed = { value: null, next: null }
    if (type === 'i') { // number (we only support ints)
      serialized.shift()
      parsed = parseNumber()
      obj.push(parsed.value)
    } else if (type === 's') { // string
      serialized.shift()
      const { value: len, next } = parseNumber()
      parsed = parseString(len)
      obj.push(parsed.value)
    } else if (type === 'a') { // assocative array (map)
      serialized.shift()
      const { value: len, next } = parseNumber()
      serialized.shift()
      const childObj = []
      obj.push(childObj)
      parse(childObj, [...parents, obj])
    } else if (type === '}') {
      parse(parents[parents.length - 1], parents.slice(0, parents.length - 1))
    } else if (type === 'b') { // boolean
      serialized.shift()
      parsed = parseBool()
    } else if (type === 'N') { // null
      parsed = { value: null, next: serialized.shift() }
    } else {
      console.error(obj)
      throw new Error("unsupported serialized type " + type + obj.join(" "))
    }
    if (parsed.next === ';') {
      parse(obj, parents)
    }
    return obj
  }

  const associativeArrayToMap = (arr) => {
    const map = {}
    const len = arr.length
    for (let i = 0; i < len / 2; i++) {
      let [key, val] = arr.splice(0, 2)
      if (Array.isArray(val)) {
        val = associativeArrayToMap(val)
      }
      map[key] = val
    }
    return map
  }
  
  return associativeArrayToMap(parse(res)[0])
}