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

Installation | Usage | Annotated source | License

NPM version KLP


npm install not-defined


This snippet of code

const notDefined = require('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

const no = require('not-defined')

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

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


Annotated source

This is my first npm package written using KISS Literate Programming. It is plain ES5 function that is 159 characters long.

module.exports=function(x){return x==null||(typeof x == 'number'&&isNaN(x))||(x.length<1&&typeof x!='function')||(typeof x=='object'&&Object.keys(x).length<1)}

Snippet length<1 is used instead of equivalent length==0 to save two characters, considering it is used twice.