How are constants different from variables in JavaScript?
In JavaScript, constants and variables are both fundamental concepts used for storing and manipulating data. However, they differ in their characteristics and behavior. Understanding the distinctions between constants and variables is important for effective programming in JavaScript.
A constant is a value that cannot be changed after it has been assigned. It is declared using the `const` keyword, followed by a unique identifier (name), an assignment operator (`=`), and the initial value. Once a constant is assigned, its value remains fixed throughout the program execution. Any attempt to modify the value of a constant will result in an error.
For example, consider the following code snippet:
const PI = 3.14159;
In this case, `PI` is a constant that represents the mathematical constant pi. The value of `PI` cannot be altered later in the program.
On the other hand, a variable is a storage location that can hold different values during the execution of a program. It is declared using the `let` or `var` keyword, followed by a unique identifier, an assignment operator, and an optional initial value. Unlike constants, variables can be reassigned multiple times throughout the program.
Here's an example that demonstrates the usage of a variable:
let counter = 0; counter = counter + 1;
In this code snippet, `counter` is a variable that starts with an initial value of 0. The subsequent line increments the value of `counter` by 1. Variables provide flexibility in programming as their values can change based on the requirements of the program.
One important distinction between constants and variables is their scope. Both constants and variables can have either local or global scope. Local scope means they are accessible only within a specific block of code, such as a function. Global scope means they can be accessed from anywhere within the program.
It is worth noting that constants are block-scoped, which means they are only accessible within the block of code where they are defined. Variables, on the other hand, can be block-scoped or function-scoped depending on how they are declared.
To summarize, constants in JavaScript are used to store values that remain unchanged throughout the program execution, while variables are used to store values that can be modified as needed. Constants are declared using the `const` keyword and cannot be reassigned, while variables are declared using the `let` or `var` keyword and can be reassigned multiple times. Understanding the differences between constants and variables is essential for writing robust and maintainable JavaScript code.
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