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

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

Answer 2

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.

Answer 3

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;
}

Answer 4

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".

Answer 5

That's what typeof is there for. The parentheses are optional since it is an operator.

if (typeof variable === "boolean"){
  // variable is a boolean
}

Answer 6

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;
  }