function allowedAttribute(attr, allowedAttributeList) {
    var attrName = attr.nodeName.toLowerCase();

    if (allowedAttributeList.indexOf(attrName) !== -1) {
      if (uriAttrs.indexOf(attrName) !== -1) {
        return Boolean(attr.nodeValue.match(SAFE_URL_PATTERN) || attr.nodeValue.match(DATA_URL_PATTERN));
      }

      return true;
    }

    var regExp = allowedAttributeList.filter(function (attrRegex) {
      return attrRegex instanceof RegExp;
    }); // Check if a regular expression validates the attribute.

    for (var i = 0, l = regExp.length; i < l; i++) {
      if (attrName.match(regExp[i])) {
        return true;
      }
    }

    return false;
  }
A pattern that matches safe data URLs. Only matches image, video and audio types.

Shoutout to Angular 7 https://github.com/angular/angular/blob/7.2.4/packages/core/src/sanitization/url_sanitizer.ts