for (var i of options.iframeCssUrlsAddition) { additionCssHtml.push("<link rel='stylesheet' type='text/css' href='" + utils.unhtml(options.iframeCssUrlsAddition[i]) + "'/>") }
更正
for(var iframeCss of options.iframeCssUrlsAddition){ additionCssHtml.push("<link rel='stylesheet' type='text/css' href='" + utils.unhtml(iframeCss) + "'/>") }