JavaScript Variables

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Variables are containers for storing data values. In JavaScript, you can declare variables using var, let, or const.

var

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The var keyword has been in JavaScript since the beginning. Variables declared with var are function-scoped or globally-scoped, but not block-scoped.

var name = "John Doe";
function showName() {
  var name = "Jane Doe";
  console.log(name); // "Jane Doe"
}
showName();
console.log(name); // "John Doe"

let

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The let keyword, introduced in ES6, allows you to declare block-scoped variables. This is generally preferred over var.

let x = 10;
if (true) {
  let x = 20;
  console.log(x); // 20
}
console.log(x); // 10

const

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The const keyword is also block-scoped, but it’s used for variables that shouldn’t be reassigned. The value of a const variable cannot be changed, but if the variable is an object or array, its properties or elements can be modified.

const PI = 3.14;
// PI = 3.14159; // This will cause an error

const person = { name: "John" };
person.name = "Jane"; // This is allowed
console.log(person.name); // "Jane"

Data Types

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JavaScript has several primitive data types:

• String: Represents textual data.
• Number: Represents both integer and floating-point numbers.
• Boolean: Represents true or false.
• Null: Represents the intentional absence of any object value.
• Undefined: Represents a variable that has been declared but not assigned a value.
• Symbol: A unique and immutable primitive value.
• BigInt: Represents integers with arbitrary precision.

JavaScript also has a complex data type, Object, which is used to store collections of data.