/** Tracks UTM campaign parameters from query strings, persisting history in localStorage. */
export declare class UtmFields {
    private static localStorageId;
    fields: Record<string, string>[];
    constructor();
    /**
     * Parses UTM parameters from the current URL query string.
     * @returns A record of UTM key-value pairs, or null if none are present
     */
    getUtmRecord: () => Record<string, string> | null;
    /** Returns the UTM fields history as a JSON string. */
    toString(): string;
    /**
     * Checks the query string for new UTM values and appends them to the history if changed.
     * @returns The current UTM fields array, or undefined if empty
     */
    update(): Record<string, string>[];
}
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