Let's leave the no-brainer - translating UML to skeleton class - alone.

farewell-to-uml.js

const fieldsLiteral = `- name: String
- age: int
- tumId: String`

const funcsLiteral = `+ Person(String, int, String)
+ say(String): Shit`

printAttributes(fieldsLiteral)
printFunctions(funcsLiteral)

function printAttributes(fieldsLiteral) {
  let result = ""

  for (const attribute of fieldsLiteral.split("\n")) {
    result += getAccessModifier(attribute) + getType(attribute) + getName(attribute) + ";\n"
  }
  console.log(result)
}

function printFunctions(funcsLiteral) {
  let result = ""

  for (const fn of funcsLiteral.split("\n")) {
    result += getAccessModifier(fn) + getType(fn) + getRawSignature(fn) + " {\n\n}\n\n"
  }
  console.log(result)
}

function getAccessModifier(literal) {
  const parts = literal.split(" ")
  if (parts[0] == "+") {
    return "public"
  }
  else if (parts[0] == "-") {
    return "private"
  }
  else {
    return "";
  }
}

function getType(attrLiteral) {
  if (attrLiteral.includes("void") || !attrLiteral.includes(":")) {
    return " "
  }
  return " " + attrLiteral.substring(attrLiteral.indexOf(":") + 1).trim() + " "
}

function getName(literal) {
  return literal.slice(0, literal.indexOf(":")).split(" ").slice(-1)[0]
}

function getRawSignature(funcLiteral) {
  const name = funcLiteral.substring(funcLiteral.indexOf(" ") + 1, funcLiteral.indexOf("("))
  let rawSignature = name + "("
  const paramTypes = funcLiteral.substring(funcLiteral.indexOf("(") + 1, funcLiteral.indexOf(")")).split(", ")
  let count = 0
  for (const paramType of paramTypes) {
    rawSignature += paramType + " param" + count++ + ", "
  }
  return rawSignature.substring(0, rawSignature.lastIndexOf(",")) + ")"
}