pvdz.ee - 11.4.1 delete operator

UnaryExpression : delete UnaryExpression

Code: (Meta Ecma)

function evaluate(delete UnaryExpression) {
  var ref = evaluate(UnaryExpression);
  if (Type(ref) != 'reference') return true; // no such property
  if (IsUnresolvableReference(ref)) {
    if (IsStrictReference(ref)) throw SyntaxError;
    return true; // property doesn't exist...
  }
  if (IsPropertyReference(ref)) return ToObject(GetBase(ref)).[[Delete]](GetReferencedName(ref), IsStrictReference(ref));
  // ref is environment record binding
  if (IsStrictReference(ref)) throw SyntaxError;
  var bindings = GetBase(ref);
  return bindings.DeleteBinding(GetReferencedName(ref));
}

Basically, a SyntaxError is thrown when you try to delete a variable, function or function argument directly (so not when removing a property of an object, but from the current lexical environment). Additionally, a TypeError is thrown when in strict mode and the property has the attribute [[Configurable]] set to false.

See also DeleteBindings and [[Delete]].