Destructuring, defaults, and rest parameters

The idea

Destructuring gives local names to positions or properties without changing the source. An object pattern may rename a property; an array pattern uses positions. A default expression runs when the selected value is undefined, including a missing property. It does not replace null, zero, or false. This distinction matters when a caller intentionally supplies an empty or disabled setting.

Rest parameters collect remaining arguments into an array. They work well when a function naturally accepts a variable number of values, but they do not validate those values. Destructured function parameters also need an outer default if calling with no argument should be allowed. An outer empty-object default handles undefined; passing null still cannot be destructured as an object.

function describe({size = 8, label: name = "item"} = {}) {
  return name + ":" + size;
}
console.log(describe({size: 0}));
console.log(describe());

item:0
item:8

The property default preserves zero. The parameter default supplies an object when the argument is omitted.