In programming, a constant is a value that, once assigned, cannot be changed during the execution of a program. Constants are used to represent fixed values that do not change, such as mathematical constants, configuration values, or identifiers.
Constants help improve code readability and maintainability by providing meaningful names for fixed values. They also prevent accidental modification of values that should remain unchanged.
Example in JavaScript:
// Declaration of a constant
const PI = 3.14159;
const MAX_USERS = 100;
// Usage of constants
console.log(`The value of PI is ${PI}`);
console.log(`The maximum number of users is ${MAX_USERS}`);
// Attempting to reassign a constant will result in an error
// PI = 3.14; // Uncaught TypeError: Assignment to constant variable.
In this example:
PIis a constant representing the mathematical constant pi.MAX_USERSis a constant representing the maximum number of users allowed.- Both constants are declared using the
constkeyword, and their values cannot be changed once assigned.