Basic JavaScript: Data Types

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

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:

  • Number

  • String

  • Boolean

  • Arrays

  • Object

  • null

  • undefined

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

Number

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

1var a = 2;
2console.log(typeof a); // "number"
3var b = 3.56;
4console.log(typeof b); // "number"

String

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

1var name = "Developer";
2console.log(typeof name); // string
3
4var letter = "A";
5console.log(typeof letter); // string

Boolean

A boolean is a true or false value.

1var isRaining = true;
2console.log(typeof raining); // boolean
3
4var isLoggedIn = false;
5console.log(typeof isLoggedIn); // boolean

Arrays

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

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

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

1var 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.

1console.log(colors[0]); //red
2console.log(colors[1]); //green
3
4console.log(numbers[0]); // 1
5console.log(numbers[1]); // 2

Object

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

1var obj = {
2  name: "Shubham",
3  age: 20,
4  role: "Frontend Developer",
5  isStudent: true,
6  hobbies:['coding","reading","eating"]
7};

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

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

Syntax:

  • ObjectName.keyName = if the key is a String.

  • ObjectName[keyName] = if the key is a Number

1var obj = {
2  name: "Shubham",
3  age: 20,
4  role: "Frontend Developer",
5  100: "Hundred",
6};
7
8console.log(obj.name); // "Shubham"
9console.log(obj.age); // 20
10console.log(obj[100]); // "Hundred"

null

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

undefined

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

1var a;console.log(a); // undefined

These are the basics data types present in JavaScript.

Next, we will learn about JavaScript Operators.