JavaScript typeof operator

The JavaScript typeof operator is used to return a string that represents the type of JavaScript for a given value. It returns the data type of the operand in the form of a string. The operand can be a literal or a data structure like a function, an object, or a variable.

Syntax

There are following two ways of using the typeof operator.

Values

operand: It is an expression that represents the object or primitive whose type is to be returned.

The possible return values of the typeof operator are tabulated as follows:

Type of the operand	Result
object	“object”
number	“number”
string	“string”
boolean	“boolean”
function	“function”
undefined	“undefined”

Let’s understand this operator by using some examples.

Example1

In this example, the operands are of number type. The typeof operator will print the “number” as the type of the operand, whether the operand is a negative interger, floating-point number, infinity, NaN, zero, or any integer.

  <html>  <head>  <script>  document.write(typeof (45) + “<br>”);  // results: “number”  document.write(typeof (-90) + “<br>”);  // results: “number”  document.write(typeof (0) + “<br>”);  // results: “number”  document.write(typeof (22.6) + “<br>”);  // results: “number”  document.write(typeof (Infinity) + “<br>”);  // results: “number”  document.write(typeof (NaN));  // results: “number”. Although NaN is “Not-A-Number”  </script>  </head>    <body>  </body>  </html>  

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Output

After the execution of the above code, the output will be –

number  number  number  number  number  number

Example2

In this example, the operands are of string type. The typeof operator will print the “string” as the type of the operand, whether the operand is an empty string, collection of characters, number written in quotes.

  <html>  <head>  <script>  document.write(typeof (“”) + “<br>”);  // results: “string”  document.write(typeof (“tutoraspire.com”) + “<br>”);  // results: “string”  document.write(typeof (“20”) + “<br>”);  // results: “string”  document.write(typeof (typeof 1) + “<br>”);  // results: “string”  document.write(typeof String(12));  // wrapping in String function will results: “string”  </script>  </head>    <body>  </body>  </html>  

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Output

After the execution of the above code, the output will be –

string  string  string  string  string

Example3

In this example, the operands are of Boolean type. The typeof operator will print the “boolean”, as the type of the operand, if the operand is true, or false.

  <html>  <head>  <script>  document.write(typeof (true) + “<br>”);  // results: “boolean”  document.write(typeof (false) + “<br>”);  // results: “boolean”  document.write(typeof Boolean(20) + “<br>”);   // wrapping in Boolean function will results: “boolean”  </script>  </head>    <body>  </body>  </html>  

Test it Now

Output

After the execution of the above code, the output will be –

boolean  boolean  boolean

Example4

In this example, the operands are of undefined type. The typeof operator will print the “undefined” as the type of the operand. Here, the type of Null is undefined, it is because it is written as Null instead of null. If we write it as null, the type of it will be object.

  <html>  <head>  <script>  document.write(typeof Null + “<br>”);  // results: “undefined”  document.write(typeof undefined + “<br>”);  // results: “undefined”  document.write(typeof a + “<br>”);   // results: “undefined”  </script>  </head>    <body>  </body>  </html>  

Test it Now

Output

After the execution of the above code, the output will be –

undefined  undefined  undefined

Example5

In this example, the operands are of Object and Function type. The typeof operator will print the “object” and “function”, according to the type of the operand.

  <html>  <head>  <script>  document.write(typeof null + “<br>”);  // results: “object”  document.write(typeof [1, 2, ‘hello’] + “<br>”);  // results: “object”  document.write(typeof {a: ‘hello’} + “<br>”);   // results: “object”  document.write(typeof [1, 2, 3, 4] + “<br>”);   // results: “object”  document.write(typeof function(){} + “<br>”);   // results: “function”  document.write(typeof class hello{} + “<br>”);   // results: “function”  </script>  </head>    <body>  </body>  </html>  

Test it Now

Output

After the execution of the above code, the output will be –

object  object  object  object  function  function

Next TopicJavaScript ternary operator

JavaScript typeof operator

JavaScript typeof operator

Syntax

Values

Example1

Example2

Example3

Example4

Example5

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