Let's consider a function that determines the total number of days in a given month.

`const getDays = (month, year) => {`

...

};

Since months in JavaScripts start from 0, we assume that the `month`

parameter is zero-based index. We can make the function quickly return if the month is April, June, September or November:

`if (month === 3 || month === 5 || month === 8 || month === 10) {`

return 30;

}

...

These conditionals can be replaced with a single check by using the `Array.includes`

function:

`if ([3, 5, 8, 10].includes(month)) {`

return 30;

}

...

For this specific function, we can use a lookup table:

`const isLeapYear = year => (`

(year % 4) === 0 && ((year % 100) !== 0 || (year % 400) === 0)

);

const getDays = (month, year) => (

[

31,

(isLeapYear(year) ? 29 : 28),

31, 30, 31, 30, 31, 31, 30, 31, 30, 31

][month]

);

*More*