Rhesus Negative

const books = { 
'small:green': 10, 
'small:red': 15, 
'medium:green': 20, 
'medium:red': 25, 
'large:green': 30, 
'large:red': 35 
} 

function count() { 
const 
size = document.querySelector('#size').value, 
color1 = document.querySelector('#color').value, 
amount = document.querySelector('#amount').value; 

document.querySelector('#total').textContent = `${books[`${size}:${color}`] * amount} р.`; 
} 

count(); 

document.querySelector('form').addEventListener('change', count); 

function change(objName, min, max, step) { 
var obj = document.getElementById(objName); 
var tmp = +obj.value + step; 
if (tmp < min) tmp = min; 
if (tmp > max) tmp = max; 
obj.value = tmp; 
count();
}