export declare type BasePostMessageCallbackProps<T> = {
    onMessage?: (message: T) => void;
    onInvalidMessageError?: (message: T, error: Error) => void;
};
export declare class PostMessageFieldDecodeError extends Error {
    messageType: string;
    field: string;
    expectedType: TypeDef;
    gotValue: unknown;
    constructor(messageType: string, field: string, expectedType: TypeDef, gotValue: unknown);
}
export declare class PostMessageUnknownTypeError extends Error {
    postMessageType: string;
    constructor(postMessageType: string);
}
export declare type MessageEventData = {
    mx?: boolean;
    metadata?: Metadata;
    type?: string;
};
declare type FieldProperties = {
    optional?: boolean;
};
export declare type Value = string | number | boolean;
export declare type NestedValue = Record<string, Value>;
export declare type Metadata = Record<string, Value | NestedValue>;
export declare type TypeDef = string | Array<string> | Record<string, string>;
export declare function assertMessageProp(container: Metadata, postMessageType: string, field: string, expectedType: TypeDef, properties?: FieldProperties): void;
export {};