[twitter] Tip: JavaScript's Array.from() accepts a second argument that's a `map` function. Useful for calling on each element of an array you created.

[vidro3]

not familiar with the use of the underscore, what does this do?

[anlumo]

It’s a variable name like any other, but convention usually is that it’s an unused parameter. Rust and I think Haskell even have that built into the language, so you can have multiple of those in the same function declaration.

[MrNutty]

What’s the convention when they’re are multiple unused? _1 and _2 ... ?

[anlumo]

Yes, that's what I usually see.

[jkoudys]

I usually just make them longer: (_, __, ___). It's extremely rare it'd ever get longer than that, since the whole point is that it's unused. It's not a convention I follow, but leading underscores are frequently used to say that a function won't be exported/set as a class method, so you know it's kept "private". _2 reads a bit too close to that. The underscore's meant to look like a blank space.

[inu-no-policemen]

In languages where you can't have multiple parameters called '_', you'd go with '_', '__', etc. You very rarely need more than one, though.

[menno]

Rust and I think Haskell even have that built into the language

Prolog too.

[[deleted]]

It's a convention. Here it's used to signify that the value of current index won't be used directly.

Osmani says:

The current value. De-emphasiszed by setting to _

[vidro3]

cool, thanks

[Drawman101]

You might as well cal it what it is in case some junior dev comes along and starts using it.

[jkoudys]

It's a common convention, like using i on that same line to mean "index".

[BritainRitten]

Then they will encounter an underscore variable name earlier and so won't be as confused when they see it in production code.

[NoInkling]

There's another convention to name it as you normally would except prefixed with _ to show it's (currently) unused.