Spec allows missing initializer in destructuring lexical bindings

[nickie]

TypeScript's specification seems to allow a missing initializer for destructuring lexical bindings, whereas the EC262 specification does not. Is this intentional? In that case, I believe it should only be allowed in the case that a type annotation is present, e.g., in let [x, y]: number[]; The current playground implementation seems to disallow this.

[RyanCavanaugh]

The initializer for DestructuringLexicalBinding should not be opt