JavaScript Variables with Examples

In JavaScript, a variable is a container that can hold a value or a reference to a value. Variables are used to store and manipulate data within a program.

There are three ways to declare a variable in JavaScript:

var: This is the original way to declare a variable in JavaScript. It is used to declare a variable that is function-scoped. That is, it can be accessed within the function in which it is declared, as well as any nested functions.

Example:

function myFunction() {
  var x = 5;
  console.log(x); // Output: 5
}

let: This is a relatively new way to declare a variable in JavaScript. It is used to declare a variable that is block-scoped. That is, it can be accessed only within the block in which it is declared (including any nested blocks).

Example:

function myFunction() {
  if (true) {
    let x = 5;
    console.log(x); // Output: 5
  }
  console.log(x); // Output: ReferenceError: x is not defined
}

const: This is also a relatively new way to declare a variable in JavaScript. It is used to declare a variable that is block-scoped, like let. However, once a value is assigned to a const variable, it cannot be reassigned.

Example:

function myFunction() {
  const x = 5;
  x = 6; // Error: Assignment to constant variable.
}

It's important to note that variables in JavaScript are dynamically typed, meaning that the type of a variable can change at runtime based on the value assigned to it.