JavaScript Data Types

JavaScript's versatility in handling various data formats is a key feature that contributes to its power. JavaScript allows programmers to create sophisticated applications and interactive websites because it supports a wide variety of data types, from strings and numbers to arrays and objects.

Because JavaScript is a dynamically typed language, we don't need to declare the type of a variable before using it, which is one of its great features. As a result, whatever value was assigned to a variable, the variable's type changed as a result of the assigned value.

Variables in JavaScript can be given values of various data types at various points while a program is being executed. A variable might be given a string value at one point and a numeric value at another. Because of its adaptability, JavaScript is a strong and useful language, but it can also cause unexpected behavior if not used carefully.

Primitive data types in JavaScript are the most fundamental data types and include:

Numbers: Numerical values such as integers, decimals, and even NaN (Not-a-Number) are stored in numbers.
Strings: Text values are stored in strings, which can contain single or double quotes.
Booleans: Booleans are used to store values such as true or false.
Undefined: Variables that have been declared but not yet given a value are referred to as undefined.
Null: When a variable has been explicitly given the value "null," it denotes intentional absence of any object value, but it is still a value.

JavaScript supports reference data types in addition to primitive data types, such as:

Objects: Collections of key-value pairs are kept in objects.
Arrays: Arrays are used to store groups of data in a predetermined order.
Functions: Functions are used to store chunks of code that can be run repeatedly.

For example:

x = "codescracker";    // x is of string type
x = 120;               // now x is of number type
x = true;              // now x is of boolean type

See the above example; there is no need to declare the type of a variable before initializing any value of that type.

JavaScript typeof: find the data type of a variable or value

The JavaScript typeof operator is used to find the type of value or variable. For example:

HTML with JavaScript Code

<!DOCTYPE html>
<html>
<body>

   <p id="para1"></p>
   <p id="para2"></p>
   <p id="para3"></p>
   <p id="para4"></p>
   <p id="para5"></p>
   
   <script>
      document.getElementById("para1").innerHTML = typeof "codescracker";
      document.getElementById("para2").innerHTML = typeof 10;
      document.getElementById("para3").innerHTML = typeof true;
      document.getElementById("para4").innerHTML = typeof [1, 2, 3, 4, 5];
      document.getElementById("para5").innerHTML = typeof function () {};
   </script>
   
</body>
</html>

Output

JavaScript allows three keywords to declare a variable: var, let, and const.

Consider the following code as another example demonstrating the "typeof" operator in JavaScript:

HTML with JavaScript Code

<!DOCTYPE html>
<html>
<body>

   <p id="para1"></p>
   <p id="para2"></p>
   
   <script>
      let x = 10;
      document.getElementById("para1").innerHTML = typeof x;
      document.getElementById("para2").innerHTML = typeof "codescracker";
   </script>
   
</body>
</html>

Output

The syntax of the typeof operator in JavaScript is:

typeof x