Types and Values

JavaScript is Dynamically-typed language meaning the interpreter assigns variables a type at runtime based on the variable's value at the time.

Thus, JavaScript provide special keyword called typeof to get the type of the value.

console.log(typeof undefined)
// undefined

console.log(typeof "hello")
// string

console.log(typeof 11)
// number

console.log(typeof true)
// boolean

console.log(typeof {})
// object

Primitives

Every programing language support different type of values, for different purpose. The most fundamental of them are called Primitives.

Let's look at the most popular one.

Strings

In JavaScript, Strings are values made up of text and can contain letters, numbers, symbols, punctuation, and even emojis!

Let's look at different type of strings.

console.log(typeof "hello!!")

console.log(typeof "7")

console.log(typeof "")

console.log(typeof " ")

console.log(typeof new Date())

Numbers

Numbers are values that can be used in mathematical operations. You don’t need any special syntax for numbers — just write them straight into JavaScript.

console.log(7)
// number
console.log(3.14159265359)
// number

// But what's the limit, well you can check like this
console.log(Number.MAX_SAFE_INTEGER)
// 9007199254740991
console.log(Number.MIN_SAFE_INTEGER)
// -9007199254740991

NOTE: More on Number later. But if you're curious, then read the source.

Booleans

They are rather simple, they can only be true and false.

console.log(typeof true)

console.log(typeof false)

Objects

Objects are variables that contain multiple data values. The values within a JS object are known as properties. Objects use keys to name values, much like how is done with variables.

Objects are first Reference value/type we have encountered so far. Just keep that in mind we'll discuss it later.

// Objects are defined using `{}`, and between those parenthesis lies key-value pairs.
console.log(typeof {key1: "value1", key2: "value2"})

// Well Arrays are also objects
console.log(typeof [])

// And so is null
console.log(typeof null)

Undefined & Null

undefined is default value for every variable till, it is defined. And undefined indicates the absence of a value.

While null indicates the absence of an object

Array

Array are special type of object. That hold other values in order.

The values inside an array are called elements.

Array elements don’t all have to be the same type of value. Elements can be any kind of JavaScript value — even other arrays or objects.

// Arrays are defined using `[]`, and between those brackets lies values.
console.log(typeof [1,2,3,4,5])
// object

console.log(typeof ["Naruto", "Sasuke", "Kakashi"])
// object

console.log(typeof ["Naruto", 1, true, {}, null, undefined])
// object

NOTE: You can also read about Map, Set, BigInt and Symbol. But we don't have to worry about them right now.