OptionalJS provides a functional Optional, for JavaScript.

About

The Optional is loosely based upon the Java8 Optional class. Like the Java8 version, it is not recommended to use the Optional like this:

const myopt = Optional.of("myvalue");
if(myopt.hasValue()) {
  console.log("the optional has the value ", myopt.getDirect());
}

Although the above is perfectly legal, it is recommended to use one of the many alternatives described below.

Howto

using optionaljs

Add optionaljs as a dependency to package.json: yarn add optionaljs or npm install optionaljs

Use optional in your code:

// ecmascript 2015 / ES6
import Optional from "optionaljs";

// pre ecmascript 2015 / ES6
var Optional = require("optionaljs");

Creating the Optional

Creates an Optional with a value:

const myopt = Optional.of("myvalue");

Creates an empty Optional:

const myopt = Optional.empty();

Testing for a value

please try to avoid doing this:

if(myopt.hasValue()) { 
  // ... 
}

Getting the value: the wrong way

please try to avoid doing this:

const value = myopt.getDirect();

Getting the value: the right way

Using a Promise

myopt.get()
  .then(value => console.log("the value is", value))
  .catch(() => console.log("the Optional does not have a value"));

Using a function a argument

myopt.ifPresent(value => console.log("the value is", value));

With an alternative value

const myopt = Optional.of("fizzbuzz");
const value = myopt.orElse("foobar"); // value = "fizzbuzz" 

const myopt = Optional.empty();
const value = myopt.orElse("foobar"); // value = "foobar" 

Returning the value of another function if nor present

const myopt = Optional.of("fizzbuzz");
const value = myopt.orElseGet(() => "foobar"); // value = "fizzbuzz" 

const myopt = Optional.empty();
const value = myopt.orElseGet(() => "foobar"); // value = "foobar" 

JavaScript ....

... and since functions are first-class citizens in JavaScript, one can get really crazy ;-)