Misago/frontend/src/utils/is-url.js

const URL_PATTERN = new RegExp('^(https?:\\/\\/)?((([a-z\\d]([a-z\\d-]*[a-z\\d])*)\\.)+[a-z]{2,}|((\\d{1,3}\\.){3}\\d{1,3}))(\\:\\d+)?(\\/[-a-z\\d%_.~+]*)*(\\?[;&a-z\\d%_.~+=-]*)?(\\#[-a-z\\d_]*)?$','i');

export default function(str) {
  return URL_PATTERN.test($.trim(str));
}