Log a variable in an arrow function

Have you ever had to debug an 1 line arrow function using `console.log`? It usually requires us to switch to a multiple lines version such as:

const formatYmd = (date) => {
    console.log(date.toISOString());
    return date.toISOString().slice(0, 10);
};

You can get rid of that conversion by using the `||` operator. It works because `console.log()` returns `undefined`, so the `||` will enforce the function to evaluate and return the right side which is our actual function.

const formatYmd = (date) => console.log(date.toISOString()) || date.toISOString().slice(0, 10);

formatYmd(new Date());
// Print something like `2021-02-25T04:52:39.720Z` in the Console

There is another, less known tip which uses the comma operator:

const formatYmd = date => (console.log(...), date.toISOString().slice(0, 10));

You will find more useful 1 line-of-code functions on 1 LOC

Log a variable in an arrow function

See also