Types

Numbers

JavaScript uses 64 bits to store number values

Fractional numbers

console.log(9.81)

Scientific notation

console.log(2.998e8)

Special Numbers

1. Infinity

   Infinity and -Infinity represent positive and negative infinities

   console.log(Infinity - 1)
   console.log(Infinity + 1)
   console.log(-Infinity - 1)
   console.log(-Infinity + 1)

2. NaN

   Not a number. The returned result if you try to do mathematical nonsense

   console.log(0 / 0)
   console.log(Infinity - Infinity)

Strings

Following are acceptable strings

console.log(`Down on the sea`)
console.log("Lie on the ocean")
console.log("Float on the ocean")

Backslash escapes characters

console.log("This is the first line\nAnd this is the second")
console.log('A newline character is written like "\\n".')

Backtick quoted strings (template literals) can span lines and also embed other values. \${} in a template literal will be computed and converted to a string

console.log(`This is a
backtick quotes string`)
console.log(`half of 100 is ${100 / 2}`)

Boolean

console.log(3 > 2)
console.log(3 < 2)

Strings can also be compared

console.log("Aardvark" < "Zoroaster")

Uppercase characters are always less than lower case characters, so "Z" \< "a". Non alphabetic characters are less than alphabetic characters

console.log("Zebra" < "aardvark")
console.log("!" < "aardvark")
console.log("!" < "Zebra")
console.log("3" < "Zebra")
console.log("!" < "3")

Empty values

There are two special empty values, null & undefined that denote the absence of any meaningful value. They can be used interchangeably and are an accident of JavaScripts design.

console.log(null == undefined)

ES6

Symbols

They are tokens that serve as unique IDs. You create symbols via the factory function Symbol() (which is loosely similar to String returning strings if called as a function):

const symbol1 = Symbol()

Add a description

const tralala = Symbol("tralala")
console.log(tralala) // Symbol(tralala)

Convert to string

const tralala = Symbol("tralala")
console.log(String(tralala)) // `Symbol(tralala)`

Every Symbol is unique

console.log(Symbol() === Symbol()) // false

Property keys

const KEY = Symbol()
const obj = {}

obj[KEY] = 123
console.log(obj[KEY]) // 123

const FOO = Symbol()
const obj = {
  [FOO]() {
    return "bar"
  },
}
console.log(obj[FOO]()) // bar