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/** * @name promisify * @summary Wraps an async callback into a `Promise` * @description * Wraps the supplied async function `fn` that has a standard JS callback `(error: Error, result: any)` into a `Promise`, passing the supplied parameters. When `error` is set, the Promise is rejected, else the Promise resolves with the `result` value. * @example * <BR> * * ```javascript * const { promisify } from '@polkadot/util'; * * await promisify(null, ((a, cb) => cb(null, a), true); // resolves with `true` * await promisify(null, (cb) => cb(new Error('error!'))); // rejects with `error!` * ``` */export function promisify <R = any> (self: unknown, fn: (...params: any) => any, ...params: any[]): Promise<R> {  return new Promise((resolve, reject): void => {    fn.apply(self, params.concat((error: Error | null, result?: R): void => {      if (error) {        reject(error);      } else {        resolve(result as R);      }    }));  });}