Java Optional type with JavaScript

Optional.js

class OptionalType {
  constructor (value){
    this.value = value
  }

  get() {
    return this.value
  }

  getOrElse(orElse) {
    const elseVal = orElse instanceof Function ? orElse() : orElse
    return this.isDefined() ? this.value : elseVal;
  }

  map(mapFn) {
    return this.isDefined() ? new of(mapFn(this.value)) : empty();
  }

  flatMap(mapFn) {
    return this.isDefined() ? mapFn(this.value) : empty()
  }

  isDefined () {
    return (this.value !== undefined);
  }
}

const empty = () =>
  new OptionalType()
  
const of = value =>
  (value === undefined || value === null) ?
      new empty() :
      new OptionalType(value)  

const Optional = {
  of,
  empty
}

export default Optional;

example how to use an Optional type

const toUpper = str => str.toUpperCase()

const textScraper = elem => 
   Optional
      .of(elem.match(/<p>([\s\S]*)?<\/p>/i))
      .map(elem => elem[1])
           
 const someValuee = textScraper('<p>some text</p>')
    .map(str => str.trim())
    .map(va => va + " here")
    .flatMap(str => new Optional.of(toUpper(str)))
    .map(toUpper)
    .getOrElse(() => 'there is no text to scrape')

console.log(someValuee)

result > SOME TEXT HERE

and if we change this line

const someValuee = textScraper('<p>some text</p>')

to

const someValuee = textScraper('<div>some text</div>')

result will be

result > there is no text to scrape