Concept

Data type is a system of data types used to determine the type of data for a variable.

Primitive Data Types

JavaScript supports 6 primitive data types:

Number: This data type is used to represent numbers in JavaScript.

let age = 25;
let height = 1.75;

String: This data type is used to represent character strings in JavaScript.

let name = "John Doe";
let message = 'Welcome to my website!';

Boolean: This data type has only two values, true or false.

let isStudent = true;
let isEmployed = false;

Null: This data type has only one value, null, which represents a non-existent or invalid value.

let data = null;

Undefined: This data type has only one value, undefined, which represents a variable that has not been assigned a value or does not exist.

let age;
console.log(age); // undefined

Symbol: This data type is used to create unique, immutable values.

let id = Symbol("uniqueId");

Complex Data Types

In addition to primitive data types, JavaScript also supports complex data types, including:

Array: This data type is used to store a collection of values.

let numbers = [1, 2, 3, 4, 5];
let names = ["John", "Jane", "Bob"];

Object: This data type is used to store data components with similar characteristics and behaviors.

let person = {
  name: "John Doe",
  age: 25,
  isStudent: true
};

Function: This data type is used to define code blocks that can be called and executed.

function greet(name) {
  console.log("Hello, " + name + "!");
}

greet("John"); // Hello, John!

Type Casting

JavaScript provides methods to typecast between different data types.

let age = 25;
let ageAsString = String(age); // Chuyển số thành chuỗi

let height = "1.75";
let heightAsNumber = Number(height); // Chuyển chuỗi thành số

let isStudent = true;
let isStudentAsString = String(isStudent); // Chuyển boolean thành chuỗi