🟨JavaScript numbers

Number type

JavaScript's Number type encompasses all kinds of numbers and special cases of numbers:

• simple integers (e.g. -2, -1, 0, 1, 2)

• floating point decimals (e.g. 0.36, -25.19111)

  • aka "floats"

• infinity (i.e. Infinity, e.g. dividing a Number by 0)

• non-number (i.e. NaN, e.g. dividing a String by a Number)

Other programming languages might have separate types for each kind of number

JavaScript also supports other number bases, i.e.:

• binary (base 2, i.e. only 0 and 1)

• octal (base 8, i.e. numbers 0 to 7)

• hexadecimal (base 16, i.e. numbers 0 to 9 and a to f)

  • handy for color hex codes

Adding Numbers to Strings

In JavaScript, if we try to add a Number to a String, JavaScript will convert the Number part of the equation into a String like such:

const mixedEquation = '10' + 5 
// '105'

console.log(typeof mixedEquation) 
// string

Other operations with mixed Numbers and Strings

However, if we try to perform subtraction, multiplication or division operations with a Numberand a String, JavaScript will try to convert the String into a Number!

const mixedSub = '10' - 5
// 5

const mixedMul = 2 * '8'
// 16

const mixeddiv = 10 / '4'
// 2.5

Operations with mixed Numbers and Booleans

Now, how about the crazy idea of performing arithmetic with a Numberand a Boolean(a trueand falsevalue)? Well, truebecomes 1 and falsebecomes 0!

const crazyAdd = 2 + true
// 3

const crazySub = 2 + false
// 2

Methods for Numbers and related

isNaN(input)

Takes in any input as a parameter and returns either trueor falseif a number exists:

const something = "12"
console.log(isNaN(something))
// true ... something is NaN because it's a String!

const somethingElse = 12
console.log(isNaN(somethingElse))
// false ... 12 is a number!

Oddly enough, NaN is a Number in JavaScript! Try it with typeof NaNin the console!

Another fun thing to try : NaN === NaN will be false!

Another edge case includes:

console.log(isNaN("")) 
// false

This happens since isNaN()tries to convert any passed-in value (argument) into a Numberfirst. in the case of an empty string, JavaScript will convert that into a 0 . Thus, the empty string is actually considered a Number!

In ES6, Number has a separate isNaN()built-in method, Number.isNaN(), to address this issue:

console.log(Number.isNaN(""))
// true

Thus, the Number.isNaN() differes in that it does not coerce the argument into a Number at all!

parseFloat(input)

Takes in any input and tries to find a floating-point decimal number at its beginning:

const something = "1.99 is the price of everything in this store!"
console.log(parseFloat(something))
// 1.99

const somethingElse = "text at the beginning of 1.99"
console.log(parseFloat(somethingElse))
// NaN

const somethingSpacey = "     2000.00 still works"
console.log(parseFloat(somethingSpacey))
// 2000

const somethingSigned = "-22.09 will work"
console.log(parseFloat(somethingSigned))
// -22.09

If the first parts of the Stringare non-numeric, it will usually return NaN,but JavaScript will still try to ignore whitespace and the unary operators ( +and - signs)!

parseInt(input)

Similar to `parseFloat`, parseInt stops looking after the first non-digit. It also returns only the integer portion of a floating-point decimal number, with parsing rules similar to the parseFloat:

const something = "1.99 is the price of everything in this store!"
console.log(parseInt(something))
// 1

const somethingElse = "of course you know this will be NaN and not 99!"
console.log(parseInt(somethingElse))
// NaN

const somethingSpacey = "     2000.00 still works of course"
console.log(parseInt(somethingSpacey))
// 2000

const somethingSigned = "-22.09 will work but chop off the decimals"
console.log(parseInt(somethingSigned))
// -22

Number.toFixed(places)

This converts numbers with a lot of decimal places, such as 3.1415926535 (pi) into a fixed number of decimal places, with rounding included:

let pi = 3.1415926535

console.log(pi.toFixed(2))
// "3.14"

console.log(pi.toFixed(3))
// "3.142"

console.log(pi.toFixed(4))
// "3.1416"

console.log(pi.toFixed())
// "3" (defaults to 0 decimal places)

Note that the toFixed() method returns a String and not a Number as the primary use case for this result is to display the value rather than perform further calculations