js怎么计算加减乘除

let a = 10;
let b = 20;
let sum = a + b; // sum 的值为 30

let a = 30;
let b = 15;
let difference = a - b; // difference 的值为 15

let a = 5;
let b = 6;
let product = a * b; // product 的值为 30

let a = 20;
let b = 4;
let quotient = a / b; // quotient 的值为 5

let a = 20;
let b = 0;
let quotient = b !== 0 ? a / b : null; // 如果 b 为 0，则 quotient 为 null

let items = [
    { name: 'item1', price: 10, quantity: 2 },
    { name: 'item2', price: 15, quantity: 1 },
    { name: 'item3', price: 5, quantity: 3 }
];

let total = items.reduce((acc, item) => acc + (item.price * item.quantity), 0);
console.log(total); // 输出购物车总价