How to check if type is Boolean

Question

How can I check if a variable s type is of type Boolean   I mean  there are some alternatives such as   if jQuery type new Boolean        jQuery type variable           Do something     But that doesn t seem pretty to me   Is there a cleaner way to achieve this

User · Answer

Sometimes we need a single way to check it. typeof not working for date etc. So I made it easy by

Date.prototype.getType() { return "date"; }

Also for Number, String, Boolean etc. we often need to check the type in a single way...

User · Answer

With pure JavaScript  you can just simply use typeof and do something like typeof false or typeof true and it will return  boolean      But that s not the only way to do that  I m creating functions below to show different ways you can check for Boolean in JavaScript  also different ways you can do it in some new frameworks  let s start with this one   function isBoolean val       return val     false    val     true      Or one-line ES6 way      const isBoolean   val   gt   boolean      typeof val    and call it like   isBoolean false     return true   Also in Underscore source code they check it like this with the    at the start of the function name    isBoolean   function obj       return obj     true    obj     false    toString call obj        object Boolean         Also in jQuery you can check it like this   jQuery type true     return  boolean    In React  if using propTypes  you can check a value to be boolean like this   MyComponent propTypes       children  PropTypes bool isRequired      If using TypeScript  you can use type boolean also   let isDone  boolean   false    Also another way to do it  is like converting the value to boolean and see if it s exactly the same still  something like   const isBoolean   val   gt    val     val    or like   const isBoolean   val   gt  Boolean val      val    and call it   isBoolean false     return true   It s not recommended using any framework for this as it s really a simple check in JavaScript

User · Answer

There are three  vanilla  ways to check this with or without jQuery    First is to force boolean evaluation by coercion  then check if it s equal to the original value   function isBoolean  n         return   n     n     Doing a simple typeof check   function isBoolean  n         return typeof n      boolean      Doing a completely overkill and unnecessary instantiation of a class wrapper on a primative   function isBoolean  n         return n instanceof Boolean       The third will only return true if you create a new Boolean class and pass that in   To elaborate on primitives coercion  as shown in  1   all primitives types can be checked in this way    Boolean   function isBoolean  n         return   n     n     Number   function isNumber  n         return  n     n     String   function isString  n         return    n     n

User · Answer

The most readable  val     false    val     true  Also readable  typeof variable    typeof true  The shortest  but not readable at all    val     val   Explanation         The double exclamation mark converts the value into a Boolean        The triple equals test for strict equality  both the type  Boolean  and the value have to be the same  If the original value is not a Boolean one  it won t pass the triple equals test  If it is a Boolean variable  it will pass the triple equals test  with both type  amp  value     Tests      5     5    false    test       test     false let val   new Date      val     val    false    true     true    true   false     false    true

User · Answer

You can create a function that checks the typeof for an argument   function isBoolean value      return typeof value      boolean

User · Answer

That s what typeof is there for  The parentheses are optional since it is an operator   if  typeof variable      boolean         variable is a boolean

User · Answer

If you just want to check for a primitive value  typeof variable      boolean    If for some strange reason you have booleans created with the constructor  those aren t really booleans but objects containing a primitive boolean value  and one way to check for both primitive booleans and objects created with new Boolean is to do    function checkBool bool        return typeof bool      boolean                  typeof bool      object   amp  amp               bool     null             amp  amp             typeof bool valueOf        boolean         x000D   x000D  function checkBool bool    x000D      return typeof bool      boolean      x000D              typeof bool      object   amp  amp   x000D              bool     null             amp  amp  x000D             typeof bool valueOf        boolean    x000D    x000D   x000D  console log  checkBool   string                  false  string x000D  console log  checkBool   test   this             false  object x000D  console log  checkBool  null                     false  null x000D  console log  checkBool  undefined                false  undefined x000D  console log  checkBool  new Boolean true         true x000D  console log  checkBool  new Boolean              true x000D  console log  checkBool  true                     true x000D  console log  checkBool  false                    true x000D   x000D   x000D

User · Answer

The most reliable way to check type of a variable in JavaScript is the following   var toType   function obj      return      toString call obj  match   s  a-zA-Z      1  toLowerCase     toType new Boolean true      returns  boolean  toType true      returns  boolean    The reason for this complication is that typeof true returns  boolean  while typeof new Boolean true  returns  object

User · Answer

if   true    yes    1   includes single value         return  true       else if   false    no    0   includes single value         return  false        if you have a string

User · Answer

BENCHMARKING  All pretty similar    const   performance     require  perf hooks     const boolyah   true  var t0   0  var t1   0  const loops   1000000  var results     1  0  2  0  3  0  4  0     for  i   0  i  lt  loops  i           t0   performance now        boolyah     false    boolyah     true      t1   performance now        results  1      t1 - t0       t0   performance now         boolean      typeof boolyah      t1   performance now        results  2      t1 - t0       t0   performance now          boolyah     boolyah      t1   performance now        results  3      t1 - t0       t0   performance now        Boolean boolyah      boolyah      t1   performance now        results  4      t1 - t0     console log results         RESULTS       0   135 09559339284897        1   136 38034391403198        2   136 29421120882034        3   135 1228678226471        4   135 11531442403793

User · Answer

I would go with Lodash  isBoolean checks whether the passed-in variable is either primitive boolean or Boolean wrapper object and so accounts for all cases

User · Answer

In nodejs by using node-boolify we can use isBoolean             var isBoolean   require  node-boolify   isBoolean          isBoolean true     true         isBoolean  true      true         isBoolean  TRUE      false         isBoolean 1     true         isBoolean 2     false         isBoolean false     true         isBoolean  false      true         isBoolean  FALSE      false         isBoolean 0     true         isBoolean null     false         isBoolean undefined     false         isBoolean      false         isBoolean        false

User · Answer

One more decision with es2015 arrow function  const isBoolean   val   gt  typeof val      boolean

User · Answer

If you want your function can validate boolean objects too  the most efficient solution must be   function isBoolean val      return val     false    val     true    val instanceof Boolean

User · Answer

You can use pure Javascript to achieve this   var test   true  if  typeof test      boolean      console log  test is a boolean

User · Answer

Creating functions like isBoolean which contains oneliner typeof v      boolean  seems very unhandy in long term  i am suprised that almost everyone suggest to create your own function  It seems to be same cancer as extending native prototypes    you need to recreate them in every project you are involved other developers might have different habits   or need to check source of your function to see which impementation of check you use  to know what are weak points of your check you will be fruustrated when you will try to write one liner in console on site which doesn t belong to your project   just memoize typeof v      boolean  and that s all   Add a template to your IDE to be able to put it by some three letter shortcut and be happy

[javascript] How to check if type is Boolean

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