How to use the card.displayBackCardByDefault function in card

reset(spec = {}) {
        this.$element = undefined;
        this._config = Object.assign({}, DEFAULT_CONFIG, spec.config);
        this.data = spec.data || {};

        const imageHeight = (this.data.summary && !this._config['card.displayLargeImage']) ?
            undefined : this.initialWidth - 10; // card margins from css TODO: move css to config object

        this.headerImage.reset({ imageUrls: this.data.imageUrl, imageHeight: imageHeight, config: this._config });
        this.readerContent.reset({ data: this.data, config: this._config });
        this.forward(this.readerContent);

        this.isExpanded = false;
        this.isFlipped = this._config['card.displayBackCardByDefault'];
        return this;
    }

render() {
        const noImages = !this.data.imageUrl && (this.data.source || this.data.sourceUrl);
        const displayBackCardByDefault = this._config['card.displayBackCardByDefault'];
        const disableFlipping = this._config['card.disableFlipping'];
        const enableBoxShadow = this._config['card.enableBoxShadow'];
        const metaDataFontSize = this._config['card.metadata.fontSize'];
        const metaDataTitleColor = this._config['card.metadata.title.color'];
        const metaDataTitleFontFamily = this._config['card.metadata.title.fontFamily'];
        const metaDataValueColor = this._config['card.metadata.value.color'];
        const metaDataValueFontFamily = this._config['card.metadata.value.fontFamily'];

        const data = Object.assign({
            titleOnly: noImages,
            boxShadow: enableBoxShadow,
            width: this.isExpanded ? this.expandedWidth : this.initialWidth,
            height: this.height,
            expandedWidth: this.expandedWidth,
            cardContentWidth: this.initialWidth,
            isExpanded: this.isExpanded,