c3_chart_fn.resize = function (size) {
    var $$ = this.internal, config = $$.config;
    config.size_width = size ? size.width : null;
    config.size_height = size ? size.height : null;
    this.flush();
};

c3_chart_fn.flush = function () {
    var $$ = this.internal;
    $$.updateAndRedraw({withLegend: true, withTransition: false, withTransitionForTransform: false});
};

c3_chart_fn.destroy = function () {
    var $$ = this.internal;

    window.clearInterval($$.intervalForObserveInserted);
    window.onresize = null;

    $$.selectChart.classed('c3', false).html("");

    // MEMO: this is needed because the reference of some elements will not be released, then memory leak will happen.
    Object.keys($$).forEach(function (key) {
        $$[key] = null;
    });

    return null;
};