constructor(opt_replacer, opt_reviver) {
    asserts.assert(goog.global['JSON'] !== undefined, 'JSON not defined');

    /**
     * @type {!Replacer|null|undefined}
     * @private
     */
    this.replacer_ = opt_replacer;

    /**
     * @type {!Reviver|null|undefined}
     * @private
     */
    this.reviver_ = opt_reviver;
  }
@param {?Replacer=} opt_replacer An optional replacer to use during
    serialization.
@param {?=} opt_reviver An optional reviver to use during
    parsing.