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Log a variable in an arrow function

Written byPhuoc Nguyen
25 Feb, 2021
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) => {
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 the 1 LOC series.

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Phước Nguyễn