2-DataTypes.md

Data Types in Javascript

Javascript - A dynamically typed language

Javascript is what you would call a dynamically typed language. What that means is a variable in Javascript can hold any type of value. To draw some context, in other statically typed languages like C, C++ or Java, you are required to specify what type of value a variable you are creating can hold.

In C, if you want to create a variable,

int a = 10;

a = 20; // This operation is allowed since 20 is a integer too.
a = 'Hello World!' // This operation will throw an error, since it's a string

In Javascript, there is no such requirement. The let keyword can be used to hold any type of value.

let a = 10;
let b = 10.5;
let c = "Hola Amigo!";

// All valid operations! 🎉

Data Types

While variables in Javascript don't have types, the values that you store in them do. What that means is the a value stored in a variable can be of the following types:

• number (A numeric value like 10 or 5.5)
• boolean (A conditional value like true or false)
• string (A character or string value like 'Hey')
• undefined (An undefined value)
• object (An aggregate value of properties and values)

number

A value of type number is any numeric value. There is not distinction in Javascript between integers and floating point numbers as in other languages. Whether the value is 5 or 5.5, both are deemed to be of type number.

let a = 10; // Value is of type number
a = 4.5; // Value is still of type number

boolean

A value of type boolean can either be true or false. Boolean values are also called the logical type since its primary use is for logical operations. A boolean value is usually the outcome of a comparison operation.

let yes = true;
let no = false;

let answer = 4 > 5;

console.log(answer); // This will print false to the console.

answer = 5 > 4;

console.log(answer); // This will print true to the console.

string

A value of type string is any character or string of characters. There are three ways you can denote a string value

• Using single quotes, 'Hi 👋'
• Using double quotes, "Hi 👋"
• Using backticks, `Hi 👋`

let first = 'Charmander';
let second = "Charmeleon";
let third = `Charizard`;

// All valid values of type string

Pro Tip 💡: While there is no difference between single and double quotes for defining your strings, the convention is to be consistent with the type of quotes you use in your javascript code (preferable single quotes 😛). Backticks help you create something called template literals.

Let's say we need to print the first name (stored in a variable called firstName) and the last name (stored in a variable called lastName) as a single name. To concatenate two strings, we can use the + operator.

let firstName = 'Tony';
let lastName = 'Stark';

console.log('My name is ' + firstname + ' ' + lastName); // This will print 'My name is Tony Stark' to the console.

However, with template literals, we can directly replace the variables inside the string! This type of value replacement inside strings is known as interpolation.

let firstName = 'Tony';
let lastName = 'Stark';

console.log(`My name is ${firstName} ${lastName}`); // This will print 'My name is Tony Stark' as well!

undefined

undefined is a rather funny value type. It denotes that the variable has not yet been assigned a value. If a variable is declared but not assigned a value, then it's value is automatically undefined.

let a;

console.log(a); // This will print undefined to the console

a = 10; // Assigning a value to a

console.log(a); // a is not longer undefined

Objects

Objects, objects ... objects? We'll cover this in the next section shall we? There's a lot to talk about here. 🤓

The typeof operator

Javascript has a handy typeof operator that tells you what the type of value stored in a variable is.

let a = 10;

console.log(typeof a); // this will print number to the console

🕵 Test your skills!

Think of the answer before executing it yourself, execute it and see if you got it right! Questions marked with a 🚀 are slightly tricky.

What do you think will be the output of the following?

let a = 10;

console.log(typeof a);

let a = 'Hello World';

console.log(typeof a);

let a = 4.5;

console.log(typeof a);

let a;

console.log(typeof a);

3. 🚀

let a;

console.log(typeof (typeof a));