Basic JavaScript: Data Types

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Data Types are important concepts in any language. They define the type of data a variable can hold.

In JavaScript, we have various data types like:

The typeof() function can be used to see the data type of the variable.


This data type can hold integers from -Infinity to +Infinity including floating-point numbers.

var a = 2;
console.log(typeof(a)); // "number"
var b = 3.56;
console.log(typeof(b)); // "number"


A String is a sequence of characters. String are denoted using " " or ' '

var name = "Developer";
console.log(typeof(name)); // string

var letter = "A";
console.log(typeof(letter)); // string


A boolean is a true or false value.

var isRaining = true;
console.log(typeof(raining)); // boolean

var isLoggedIn = false;
console.log(typeof(isLoggedIn)); // boolean


Arrays are a collection of similar data types. They are denoted using square brackets [ ]

var numbers = [1, 2, 3, 4, 5]; // array of numbers
var colors = ["red", "green", "blue"]; // array of strings

But, in JavaScript, an array can hold various data types too.

var numbersAndColors = [1, "blue", 2, "red", 3];

You can access the value of the array by its index. Every array has an index that starts with 0.

console.log(colors[0]); //red
console.log(colors[1]); //green

console.log(numbers[0]); // 1
console.log(numbers[1]); // 2


In JavaScript, an object is a collection of key: value pairs. They are denoted using the {} brackets

var obj = {
  name: "Shubham",
  age: 20,
  role: "Frontend Developer",
  isStudent: true,

Each object's key: value pair must be separated by a comma.

The data of an object can be accessed by the following syntax.


  • ObjectName.keyName = if the key is a String.
  • ObjectName[keyName] = if the key is a Number
var obj = {
  name: "Shubham",
  age: 20,
  role: "Frontend Developer",
  100: "Hundred",

console.log(; // "Shubham"
console.log(obj.age); // 20
console.log(obj[100]); // "Hundred"


A null data type means that value doesn't exist in memory.


An undefined type means that value exists but is not yet defined.

var a;
console.log(a); // undefined

These are the basics data types present in JavaScript.

Next, we will learn about JavaScript Operators.

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