ES6 Arrow Functions () vs _

Question

I tried looking this up and did not find an answer. Is there any reason to use _ over () when passing in 0 parameters in an arrow function? Just asking out of curiosity.

// ...(() => {}) vs (_ => {})

• Paul Rooney: I dont think _ is 0 parameters. It means there is an argument but you are ignoring it.
• Adam Jenkins: Very weird....saves a character I suppose.

Answer 1

The differences are:

• _ creates an identifier for the _ variable. (In rare circumstances, this may be confusing if one is using a library which assigns to window._, like underscore.js)
• Using _ means that parentheses aren't needed. (In contrast, declaring a function with zero arguments requires an empty parameter list with ()) Some like saving on a character by using _ instead.

(One could have, equivalently, used any other argument name like z which then goes unused - but the convention for an unused variable is to use _)

If one isn't using a library that assigns to window._, then the _ parameter won't shadow it, so both options work just fine. Feel free to choose whichever strikes your fancy.

Note that a common linting rule forbids the declaration of unused parameters, and will require () instead of _.

• Elitezen: Interesting, so it's basically just an unused placeholder parameter. Thanks for the info!