-------------------------------- HELPER METHODS -------------------------------- 
Adds the given meta list to the current document of the given jQuery
instance.
@private

@param {jQuery} $ - jQuery instance.
@param {Array} metaList - List of arbitrary meta objects.
function _addMetasToDoc($, metaList) {
    if (!_.isArray(metaList) || metaList.length === 0) return;
    const $head = $('head');
    let lastMeta;
    const existingMetas = $head.find('meta');
    if (existingMetas.length > 0) {
        lastMeta = existingMetas.eq(existingMetas.length - 1);
    } else {
        lastMeta = HtmlParser.DOM.N_TAB + HtmlParser.DOM.getMetaElem(metaList[0]);
        lastMeta = $head.prepend(lastMeta).find('meta');
        metaList.shift(); // remove first
    }
    metaList.forEach(metaInfo => {
        const meta = HtmlParser.DOM.N_TAB + HtmlParser.DOM.getMetaElem(metaInfo);
        lastMeta = $(meta).insertAfter(lastMeta);
    });
}