Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
Note: This interface was an attempt to create an unmodifiable list and only continues to be supported to not break code that's already using it. Modern APIs use types that wrap around ECMAScript array types instead, so you can treat them like ECMAScript arrays, and at the same time impose additional semantics on their usage (such as making their items read-only).