regexp-url

// validate url
// 检查 url 是否合法
// https://stackoverflow.com/questions/3809401/what-is-a-good-regular-expression-to-match-a-url
// http://regexr.com/3e6m0
function isUrl(url) {
  return /(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/i.test(url);
}