not-defined

checks if foo is not defined, i.e. undefined, null, an empty string, array, object or NaN

Installation

npm install not-defined

Pros

• Type less.
• Better readability (even your boss will understand your code ^:).
• Can save bytes in your builds.
• Easier to autocomplete in editors (for instance easier than typeof foo === 'undefined').

Usage

This snippet of code

import notDefined from 'not-defined'

if (notDefined(foo)) {
  // do something, usually throw a TypeError
}

is equivalent to the following pseudocode

if (foo is not defined, i.e. is null, undefined, NaN, an empty string, array or object) {
  // do something, usually throw a TypeError
}

You can also use a shorter but still semantic form like

import no from 'not-defined'

if (no(foo)) {
  // do something, usually throw a TypeError
}

A real use case: suppose you have a JSX that gets an array of items from an API. If the array of items is empty, you want to render a message.

Instead of

if (isLoading) {
  return <p>Loading...</p>
}

if (Array.isArray(items) && items.length === 0) {
  return <p>No items found</p>
}

you can write

if (isLoading) {
  return <p>Loading...</p>
}

if (no(items)) {
  return <p>No items found</p>
}

Follows a list of tested examples

no() // true
no(undefined) // true
no(null) // true
no('') // true
no([]) // true
no({}) // true
no(NaN) // true

no(0) // false
no(true) // false
no(false) // false
no('string') // false
no(['foo']) // false
no({ foo: true }) // false
no(42) // false
no(Infinity) // false
no(function () { return 1 }) // false
no(0n) // false
no(Symbol('foo')) // false

License

MIT