Filter By Truthy Values With Boolean Function

The Boolean function (not to be confused with the Boolean constructor) evaluates any given value to its boolean coercion.

> Boolean(0)
false
> Boolean(1)
true
> Boolean(null)
false
> Boolean([])
true

One way that this can be put to use is as a boolean identity function for passing to other functions like filter.

> [0, 1, "", [], "four", null, "six", undefined, 7].filter(Boolean)
[ 1, [], 'four', 'six', 7 ]

This filters out all the non-truthy values from a list.

Let's say I'm building a list of nav items that will be rendered to the UI for a specific user. Based on permissions or feature flags, certain nav items may not be available. Those "empty" entries can be filtered out in this way.

nav_items = [
  { label: "Home", href: "/" },
  isSystemAdmin && { label: "System", "/system" },
  featureEnabled(user, "api") && { label: "API", "/api" },
].filter(Boolean)

If any of those conditional nav items evaluate to false, then they will be filtered out. The resulting nav_items array is a clean list of actual nav items I want to render.