Javascript Number toMaxDecimal(d)

var k2c = k => k - 273.15
var k2r = k => k * 1.8
var k2f = k => k2r(k) - 459.67

Number.prototype.toMaxDecimal = function (d) {
 return +this.toFixed(d) + ''
}

function kCnv(k) {
 document.write( k,'K ? = ', k2c(k).toMaxDecimal(2),'C ? = ', k2r(k).toMaxDecimal(2),'R ? = ', k2f(k).toMaxDecimal(2),'F ?<br>' )
}

kCnv(21)//from  w w w .  j  a v a 2s. c  om
kCnv(295)