3.3 Empty object patterns and Array patterns

Interesting consequence of the algorithm’s rules: We can destructure with empty object patterns and empty Array patterns.

Given an empty object pattern {}: If the value to be destructured is neither undefined nor null, then nothing happens. Otherwise, a TypeError is thrown.

const {} = 123; // OK, neither undefined nor null
assert.throws(
  () => {
    const {} = null;
  },
  /^TypeError: Cannot destructure 'null' as it is null.$/)

Given an empty Array pattern []: If the value to be destructured is iterable, then nothing happens. Otherwise, a TypeError is thrown.

const [] = 'abc'; // OK, iterable
assert.throws(
  () => {
    const [] = 123; // not iterable
  },
  /^TypeError: 123 is not iterable$/)

In other words: Empty destructuring patterns force values to have certain characteristics, but have no other effects.