nil

nil is nothing. falsey. nada. zero. zip. It's a nothing thing that will eat everything you throw at it and return itself.

it does.. what?

It does a lot of nothing

var nil = require('nil');
!nil                                 // is falsey in boolean comparisons
nil == null                          // in null/undefined equality class
typeof nil == 'undefined'            // type is undefined
nil !== undefined                    // isn't undefined though
nil === nil.always.returns.nil       // all properties return nil
nil === nil()                        // returns nil when called
(nil+'') == ''                       // returns empty string when coerced to string
Object.prototype.toString.call(nil)  // '[object Nil]'
Object.keys(nil).length == 0         // returns empty array when enumerated
Object.getPrototypeOf(nil)           // null

notes

toString

In order to support coercion to empty string (instead of 'undefined') nil.toString does return a function.

var nilToString = nil.toString;
!nilToString === true                        // is NOT falsey
typeof nilToString == 'function'             // is type function
nilToString() == ''                          // returns empty string
Object.getPrototypeOf(nilToString) === nil   // inherits from nil
nilToString === nilToString.call             // call property returns self
nilToString === nilToString.apply            // apply property returns self
nilToString === nilToString.bind             // bind property returns self
nilToString === nilToString.toString         // toString property returns self
nilToString.any.other.property === nil       // because it inherits from nil
Object.keys(nilToString).length == 0         // no enumerable keys
Object.getOwnPropertyNames(nilToString) == 3 // ['call', 'apply', 'bind']

ToNumber

Because nil is typeof === 'undefined' coercion to number is unfortunately NaN. ES5 spec does not defer to valueOf to coerce undefined to a number. V8 appears to follow the spec so it seems impossible to influence the outcome of this coercion. Therefore nil isn't useful in math operations. The following is useful for this problem (with or without nil);

function toFinite(n){
  return isFinite(n *= 1) ? n : 0;
}

isObject

Common isObject functions will fail check for nil. This is probably desirable usually, but if not (like in the case of document.all), an alternative can work.

function isObject1(o){
  return Object(o) === o;
}

function isObject2(o){
  return o != null && typeof o === 'object' || typeof o === 'function';
}

function isObject3(o){
  return o == null ? o !== null && o !== undefined : typeof o === 'object' || typeof o === 'function';
}

isObject1(nil) // false
isObject2(nil) // false
isObject3(nil) // true