/**
 * A tiny and mostly spec-compliant `WebWorker` shim
 *
 * This `WebWorker` shim is implemented on top of an `IFrameElement` to allow
 * workers in contexts when `XMLHTTPRequest` is not available, or blocked by the
 * browser, e.g. when using the `file://` protocol. This shim can't provide
 * asynchronous workers, as iframes are synchronous by nature.
 */
export declare class IFrameWorker extends EventTarget implements Worker {
    protected url: URL | string;
    addEventListener: Worker["addEventListener"];
    removeEventListener: Worker["removeEventListener"];
    dispatchEvent: Worker["dispatchEvent"];
    onerror: Worker["onerror"];
    onmessage: Worker["onmessage"];
    onmessageerror: Worker["onmessageerror"];
    /**
     * The `iframe` we'll use to simulate a worker
     */
    iframe: HTMLIFrameElement;
    /**
     * A promise indicating whether the `iframe` was initialized
     */
    protected r: Promise<unknown>;
    /**
     * Create a new worker from the given URL
     *
     * @param url - Worker script URL
     */
    constructor(url: URL | string);
    /**
     * Immediately terminate the worker
     */
    terminate(): void;
    /**
     * Send a message to the worker
     *
     * @param data - Message data
     */
    postMessage(data: unknown): void;
    /**
     * Helper to retrieve the content window of the `iframe`
     *
     * If the window doesn't exist, e.g. when the `iframe` has been removed by
     * terminating the worker, an error is thrown.
     *
     * @returns Window
     */
    protected get w(): Window;
    /**
     * Internal listener that proxies message events
     *
     * @param ev - Message event
     */
    protected m: (ev: MessageEvent) => void;
    /**
     * Internal listener that proxies error events
     *
     * @param message - Error message
     * @param filename - Source filename
     * @param lineno - Source line number
     * @param colno - Source column number
     * @param error - Error object
     */
    protected e: (message?: string, filename?: string, lineno?: number, colno?: number, error?: Error) => void;
}
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