数字

• 判断奇偶数

        const isEven = num => num % 2 === 0;

        isEven(996);

• 求平均数

        const average = (...args) => args.reduce((a, b) => a + b) / args.length;

        average(1, 2, 3, 4, 5); // 3

• 指定位数四舍五入

        const round = (n, d) => Number(Math.round(n + 'e' + d) + 'e-' + d);

        round(1.005, 2) // 1.01