@fpc/types

This package exposes a few utilities for dynamic type checking.
The aim is to provide a better developer experience to users who haven't adopted
a static type system like typescript.

Consider the following code:

``javascript
const fetchWeather = () =>
fetch('https://api.weather.gov/stations/KPTK/observations/latest')
.then(resp => resp.json());

const listeners = [];

const addWeatherListener = fn =>
listeners.push(fn);

setInterval(() =>
fetchWeather().then(data =>
listeners.forEach(listener => listener(data))
)
, 10000);
`

If something that isn't a function is accidentally passed to addWeatherListener,
we'll get an error like TypeError: listener is not a function, and the stacktrace
will report the line with the listener(data) call.

Unfortunately it won't containt the call to addWeatherListener, namely
the line that mistakenly passed the wrong value, so the stacktrace is
basically useless in finding the bug.

A dynamic type check can be added in addWeatherListener to detect the wrong
type immediately:

`javascript
import { expectFunction } from '@fpc/types';

const addWeatherListener = fn =>
listeners.push(expectFunction(fn));
`

Now addWeatherListener(null) throws TypeError: Expected function, got null.

API

$3

Alias for Array.isArray

$3

Shortcut for typeof val === 'boolean'

$3

Shortcut for typeof val === 'function'

$3

Alias for Number.isSafeInteger

$3

Checks if an object implements the iterable protocol

$3

Checks if a value is a number, excludes Infinity, -Infinity and NaN.

$3

Checks if a value is a non-null object. Functions are considered objects
since in javascript they are implemented as Function object.

Functions have the same interface as every other plain object,
so there's no point in return false on functions.

E.g.:

`javascript
const obj = () => null;
obj.x1 = 10;
console.log({ ...obj, x2: 20 }); // { x1: 10, x2: 20 }
`

$3

Checks if an object is thenable.

N.b.: thenable objects may not be standard promises.

`javascript
import { isPromise } from '@fpc/types';

if (isPromise(obj)) {
obj.then(console.log, console.error); // ← this cannot fail
obj.then(console.log).catch(console.error); // catch method may not be defined
}
`

$3

Shortcut for typeof val === 'string'

$3

Shortcut for typeof val === 'symbol'

$3

Works like built-in typeof with the following differences:

- typeOf(null) === 'null'
- typeOf(NaN) === 'NaN'
- typeOf(±Infinity) === 'infinity'

$3

Every is function has an expect counterpart. For example expectInteger(5) returns 5, expectInteger(null) throws TypeError: Expected integer, got null`.