JavaScript(JS) Constants

In JavaScript, constants are variables that cannot be reassigned a new value once they are defined. The keyword used to declare a constant is const. Once a value is assigned to a constant, it cannot be changed throughout the program. Here is an example:

const PI = 3.14159;

In this example, we declared a constant named PI and assigned it a value of 3.14159. If we try to reassign a new value to PI, we will get an error:

PI = 3.14; // This will throw an error

Constants are useful for declaring values that are fixed throughout the program and should not be changed. For example, you might use a constant to represent the maximum number of characters in a text input field or the number of seconds in a minute.

Note that while the value of a constant cannot be changed, it doesn't mean that the value itself is immutable. If a constant holds a reference to an object, the properties and methods of that object can still be changed. Here is an example:

const person = { name: "John", age: 30 };
person.age = 31; // This is allowed

console.log(person); // Output: { name: "John", age: 31 }

In this example, we declared a constant named person and assigned it an object with two properties (name and age). While we cannot reassign a new value to person, we can still modify the properties of the object it references.