I have created a small Functional programming library in javascript , which supports developing code by chaining asynchronous and synchronous operations.
Consider this example
function getFromUserService({username, password}) { return new Promise((function (resolve) { resolve({name: "user", isAdmin: true}) })) } async function login(input) { if (null == input) { throw new Error("Input Cannot be Null") } const {username, password} = input if (null == username || null == password) { throw new Error("Input Cannot be Null") } const result = await getFromUserService(username, password) if (result.isAdmin) { redirectTo("adminPage") } else { redirectTo("userPage") } } The same can be rewritten as
const page = await Optional.of(input) .filter(({username, password}) => (null != username && null != password)) .map(getFromUserService) .map(result => result.isAdmin ? "adminPage" : "userPage") .toAsync(); page.ifPresentOrElse(redirectTo, () => { throw new Error("Input Cannot be Null") }) Using with Fetch
const rawResults = await fetch('https://jsonplaceholder.typicode.com/todos/' + item); const response = await rawResults.json(); if (response.completed) { return response.title } else { return null } The above can be rewritten as
return await Optional.of('https://jsonplaceholder.typicode.com/todos/' + item) .map(fetch) .map(response => response.json()) .filter(response => response.completed == true) .map(response => response.title) .getAsync(); Chaining of expressions enables the code concise and help to reasonate better, can easily be composed , combined.
Installation & Usage
npm install declarative-optional //ES6 import Optional from "declarative-optional"; //Common Js const Optional = require( "declarative-optional"); //Increment a Number , which may be null Optional.of(input) .map(val=>val+1) .get() 
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