pselect

pselect

Safely select arbitrarily nested nullable fields (with strong types).

import { select } from "pselect";

const foo = {};

const baz = select(foo, p => p.bar.baz); // No Error!
console.log(baz); // undefined

How?

pselect uses the JavaScript Proxy object and Reflection to safely select the nullable field. If Proxy support doesn't exist (ex: due to an old browser), if gracefully falls back to the less effiecient, but always available try-catch.

Installing

npm install pselect

API

select

select takes in your subject and a selector function and returns the value or undefined.

const select: <TObj, TResult>(
  subject: TObj,
  selector: (obj: TObj) => TResult
) => TResult;

Example:

import { select } from "pselect";

const foo = {};

const baz = select(foo, p => p.bar.baz); // No Error!
console.log(baz); // undefined

cselect

cselect is the curried version of the select function. It lets you write nice functional code that you can pipe and chain. (See example)

const cselect: <TObj, TResult>(
  selector: (subject: TObj) => TResult
) => (subject: TObj) => TResult;

Examples:

import { cselect } from "pselect";

const foo = {};

const getBaz = p => p.bar.baz;

console.log(getBaz(foo)); // undefined

import { cselect } from "pselect";

interface IPerson {
  name: string;
  identification?: {
    passport?: {
      passportNumber: "111";
    };
  };
}

const getPerson = (id: number) => {
  return people.find(...);
}

const passportNumber = pipe(
  getPerson,
  cselect(p => p.identification!.passport!.passportNumber),
  passportNumber => passportNumber || "NO_PASSPORT"
);

const fred: IPerson = {
  name: "fred"
};

passportNumber(fred); // NO_PASSPORT

Prior Art

• Optional (null-safe) in javascript by jpitchardo
• facebookincubator/idx

Licence

MIT