Kotrotsos

const count = 10

console.log(count.toString())    // displays '10'
console.log((17).toString())     // displays '17'
console.log((17.2).toString())   // displays '17.2'

const x = 6

console.log(x.toString(2))       // displays '110'
console.log((254).toString(16))  // displays 'fe'

Kotrotsos

const number = 123456.789

// request a currency format
console.log(number.toLocaleString('de-DE', { style: 'currency', currency: 'EUR' }))
// 123.456,79 €

// the Japanese yen doesn't use a minor unit
console.log(number.toLocaleString('ja-JP', { style: 'currency', currency: 'JPY' }))
// ￥123,457

Kotrotsos

const number = 3500

console.log(number.toLocaleString()) // Displays "3,500" if in U.S. English locale
console.log(number.toLocaleString('de-DE')) // 3.500
console.log(number.toLocaleString('ar-EG')) // ٣٬٥٠٠
console.log(number.toLocaleString('zh-Hans-CN-u-nu-hanidec')) // 三,五〇〇

Kotrotsos

let numObj = 5.123456

console.log(numObj.toPrecision())    // 5.123456
console.log(numObj.toPrecision(5))   // 5.1235
console.log(numObj.toPrecision(2))   // 5.1
console.log(numObj.toPrecision(1))   // 5

numObj = 0.000123

console.log(numObj.toPrecision())    // 0.000123

Kotrotsos

Number.isInteger(10/5) // 2 true
Number.isInteger(10/3) // 3.3333333333333335 false

Kotrotsos

let numObj = 12345.6789

(1.23e+20).toFixed(2)  // Returns '123000000000000000000.00'
(1.23e-10).toFixed(2)  // Returns '0.00'

numObj.toFixed()       // Returns '12346': note rounding, no fractional part
numObj.toFixed(1)      // Returns '12345.7': note rounding
numObj.toFixed(6)      // Returns '12345.678900': note added zeros

2.34.toFixed(1)        // Returns '2.3'

Kotrotsos

const numObj = 77.1234
console.log(numObj.toExponential()) //  7.71234e+1

// If a number has more digits than requested by the fractionDigits parameter, the number is 
// rounded to the nearest number represented by fractionDigits digits. in this case (2)
console.log(numObj.toExponential(2)) //  7.71e+1

Kotrotsos

isNaN(NaN)        // true
isNaN(undefined)  // true
isNaN({})         // true

isNaN(true)       // false
isNaN(null)       // false
isNaN(37)         // false

// strings
isNaN('37')      // false: "37" is converted to the number 37 which is not NaN

Kotrotsos

console.log(3/0) // Infinite
console.log(-3/0) // -Infinite

Kotrotsos

const x = Number.MAX_SAFE_INTEGER + 1
const y = Number.MAX_SAFE_INTEGER + 2

console.log(x === y) // true because you cannot create a larger number than MAX_SAFE_INTEGER