JavaScript typeof operator

09 Sep, 2020
Below is the example of the typeof operator.
Example:<script>// "string"document.write(typeof 'mukul'+"<br>")   // "number"document.write(typeof 25 +"<br>")   // "undefined"document.write(typeof variable)</script>
<script>// "string"document.write(typeof 'mukul'+"<br>")   // "number"document.write(typeof 25 +"<br>")   // "undefined"document.write(typeof variable)</script>
Output:string
number
undefined
string
number
undefined
In JavaScript, the typeof operator returns the data type of its operand in the form of a string. The operand can be any object, function, or variable.
Syntax:
typeof operand
OR
typeof (operand)
Note: Operand is an expression representing the object or primitive whose type is to be returned.
The possible types that exists in javascript are:
undefined
Object
boolean
number
string
symbol
function
Example:
<script>// "string"document.write(typeof 'mukul'+"<br>")   // "number"document.write(typeof 25 +"<br>")   // "undefined"document.write(typeof variable)</script>
Output:
string
number
undefined
Let’s cover all the types one by one dedicating a single code section for each code.
Example: Typeof Number, in this sample, we used ‘===’ (strict equality comparison operator) which compare value and type both and then return true or false. For example- consider the first console.log(), the js starts compiling from left to right and it first calculates the type of 25 which is ‘number’ and then compares it with ‘number’ and then finally returns true or false accordingly.
<script>   //Number  console.log(typeof 25 === 'number');  console.log(typeof 3.14 === 'number');  console.log(typeof(69) === 'number');       // log base 10  console.log(typeof Math.LN10 === 'number');   console.log(typeof Infinity === 'number');     // Despite being "Not-A-Number"  console.log(typeof NaN === 'number');    // Wrapping in Number() function  console.log(typeof Number('100') === 'number'); </script> 
Output:
Fun fact NaN which stands for not-a-number has a type of “number”.
Example: Typeof string
<script>   // string  console.log(typeof '' === 'string');  console.log(typeof 'bla' === 'string');    // ES6 template literal  console.log(typeof `template literal` === 'string');    console.log(typeof '1' === 'string');  console.log(typeof (typeof 1) === 'string');    // Wrapping inside String() function  console.log(typeof String(1) === 'string');</script> 
Output:
Examople: Typeof boolean
<script>   // Boolean  console.log(typeof true === 'boolean');  console.log(typeof false === 'boolean');    // Two calls of the ! (logical NOT) operator   // are equivalent to Boolean()  console.log(typeof !!(1) === 'boolean'); </script> 
Output:
Example: Typeof undefined
<script>   // Undefined  console.log(typeof undefined === 'undefined');    // Declared but undefined variable  console.log(typeof variable === 'undefined'); </script> 
Output:
Example: Typeof symbol
<script>   // Symbol  console.log(typeof Symbol() === 'symbol');  console.log(typeof Symbol('party') === 'symbol');  console.log(typeof Symbol.iterator === 'symbol');</script> 
Output:
Example: Typeof object
<script>   // Object  console.log(typeof {b: 1} === 'object');  console.log(typeof [1, 2, 9] === 'object');  console.log(typeof new Date() === 'object');</script> 
Output:
Example: Typeof function
<script>   // function  console.log(typeof function() {} === 'function');    //classes too are objects  console.log(typeof class C {} === 'function');   console.log(typeof Math.sin === 'function'); sin function(maths)</script> 
Output:
immukul
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