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(         


        

Answer 1

There are three "vanilla" ways to check this with or without jQuery.

1. First is to force boolean evaluation by coercion, then check if it's equal to the original value:

   function isBoolean( n ) {
       return !!n === n;
   }
   

2. Doing a simple typeof check:

   function isBoolean( n ) {
       return typeof n === 'boolean';
   }
   

3. 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;
  }