falsey

falsey

Returns true if value is falsey. Strings, arrays and arguments objects with a length of 0, and objects with no own enumerable properties are considered falsey.

Install

Install with npm:

npm i falsey --save-dev

Example

var isFalsey = require('falsey');
console.log(isFalsey('');
//=> `true`

console.log(isFalsey(0);
//=> `true`

console.log(isFalsey(null);
//=> `true`

console.log(isFalsey('nil', ['nil', 'false']); // pass special cases
//=> `true`

Why?

There are other libs that do similar things, but I wanted a lib that was geared towards options handling, so that if a user defines "null" in YAML and it's returned as a string it will still be evaluated as null - and thus falsey. See the special cases for examples.

Examples

All of the following return true

isFalsey(undefined);
isFalsey(null);
isFalsey(false);
!isFalsey(true);
isFalsey(0);
!isFalsey(1);
isFalsey('');
!isFalsey('1');
isFalsey(NaN);
isFalsey({});
!isFalsey({a: 'b'});
isFalsey([]);
!isFalsey([0]);

(function(){
  isFalsey(arguments);
}();
(function(one){
  !isFalsey(arguments);
}(0);

(function(){
  var args = [].slice.call(arguments);
  isFalsey(args);
}();
(function(one){
  var args = [].slice.call(arguments);
  !isFalsey(args);
}(0);

Special cases

There are only four "special cases", ['false', 'none', 'nil', 'null], and these are easily overridden by passing a value as a second parameter, e.g.

isFalsey(foo, []);

// other examples...
isFalsey('false');
!isFalsey('false', []); // override special cases
!isFalsey('true');
isFalsey('nil');
!isFalsey('nil', []); // override special cases
isFalsey('none');
!isFalsey('none', []); // override special cases
isFalsey('null');
!isFalsey('null', []); // override special cases

Or, pass an array of values that should return true when evaluated as falsey:

isFalsey(foo, ['no', 'nope', 'nada', 'zilch']);
// you get the point

Author

Jon Schlinkert

• github/jonschlinkert
• twitter/jonschlinkert

License

Copyright (c) 2014 Jon Schlinkert, contributors. Released under the MIT license

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This file was generated by verb-cli on July 08, 2014.