How is JavaScript an untyped language?

Front End Technology Javascript Web Development

JavaScript is an untyped language because in JavaScript the variables can hold any data type meaning that JavaScript does not have a type declaration and when the variable is created we do not need to specify any data type unlike other programming languages like Java, C#, C++, etc. which needs int, char, float, etc. to create a variable.

In JavaScript we use var, let, and const to create a variable. One of the best parts of untyped language is it gives the flexibility to reassign any type of value to a variable, it doesn't matter whether the initialized value was not the same type.

Example 1

In this example we are creating a variable named “x” and assigned a number to it and then assigned a string, and then assigned an array, and then object, undefined and null. At each step, we are printing the type of the variable “x”.


<html>
<head>
   <title> Example - JavaScript is an untyped language </title>
</head>
<body>
   <h2>JavaScript is an untyped language </h2>
   <p>Printing the type of variable after reassigning multiple data types into it.</p>
   <p id ="result"></p>
</body>
   <script>
      let x = 10;
      document.getElementById("result").innerHTML += typeof x + "<br>";
      x = "Tutorials Point"
      
      document.getElementById("result").innerHTML += typeof x + "<br>";
      x = [1, 2,3 ,4, 5, 6]
      
      document.getElementById("result").innerHTML += typeof x + "<br>";
      x = {name: "Saurabh"}
      
      document.getElementById("result").innerHTML += typeof x + "<br>";
      x = undefined
      
      document.getElementById("result").innerHTML += typeof x + "<br>";
      x = null
      
      document.getElementById("result").innerHTML += typeof x + "<br>";
      x = function(){}
      document.getElementById("result").innerHTML += typeof x + "<br>";
   </script>
</body>
</html>

Example 2

In JavaScript, we can do any operation with two distinct types of variables.

For example, if we add 2 (type: number) with “3” (type: String) then we get “22” (type: String) instead of any error this is also a feature of untyped language.


<!DOCTYPE html>
<html>
<head>
   <title> How is JavaScript an untyped language </title>
</head>
<body>
   <h2> How is JavaScript an untyped language ? </h2>
   <p>Adding two different type variables.</p>
   <p id ="result"></p>
</body>
   <script>
      let x = 2; // Number
      let y = "3" // String
      let sum = x + y;
      document.getElementById("result").innerHTML += sum + "<br>" // 23
      document.getElementById("result").innerHTML += typeof sum // String
   </script>
</body>
</html>

Example 3

In the below example, we define three variables to store three ages. We use var, let and const to define the variables.


<html>
<body>
<p id ="result"></p>
   <script>
      var age1 = 20;
      let age2 = 18;
      const age3 = 32;
      function check(age){
         if (age > 18) {
            document.getElementById("result").innerHTML +="Qualified for driving<br>";
         } else {
            document.getElementById("result").innerHTML +="Not Qualified for driving<br>"
         }
      }
      check(age1);
      check(age2);
      check(age3);
   </script>
</body>
</html>

Example 4

In the below example, we define two variables first to store a string and second to store a Boolean value. We display these two variables using the document.write().


<html>
<head>
</head>
<body>
   <script>
      const price = "Is price good?"
      var flag = true
      document.write(price+flag)
   </script>
</body>
</html>

Saurabh Jaiswal

Updated on: 11-Aug-2022

708 Views

Kickstart Your Career

Get certified by completing the course

Get Started