A RegEx to match publicly-accessible HTTP URLs. I cannot guarantee it matches every case, but it matches everything I could think of.

urlregex.js

// This snippet was based off https://gist.github.com/dperini/729294 by Diego Perini,
// and is licensed under the MIT license. My additions (notably, the IPv6 regex)
// preserve the same license with the addition that I, Diab Neiroukh, am included in
// the copyright notice. I'd also appreciate it if you could link back to this Gist.

// As usual, here's the copyright notice in full:

// Copyright (c) 2010-2018 Diego Perini
// Copyright (c) 2021 Diab Neiroukh
//
// Permission is hereby granted, free of charge, to any person
// obtaining a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without
// restriction, including without limitation the rights to use,
// copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following
// conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
// OTHER DEALINGS IN THE SOFTWARE.


const regexShort = new RegExp("^(?:(?:(?:https?):)\\/\\/)(?:\\S+(?::\\S*)?@)?(?:(?!(?:10|127)(?:\\.\\d{1,3}){3})(?!(?:169\\.254|192\\.168)(?:\\.\\d{1,3}){2})(?!172\\.(?:1[6-9]|2\\d|3[0-1])(?:\\.\\d{1,3}){2})(?:[1-9]\\d?|1\\d\\d|2[01]\\d|22[0-3])(?:\\.(?:1?\\d{1,2}|2[0-4]\\d|25[0-5])){2}(?:\\.(?:[1-9]\\d?|1\\d\\d|2[0-4]\\d|25[0-4]))|\\[(((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){6,6}[0-9a-fA-F]{1,4}|((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,6}:|((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,5}:[0-9a-fA-F]{1,4}|((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,4}(:[0-9a-fA-F]{1,4}){1,2}|((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,3}(:[0-9a-fA-F]{1,4}){1,3}|((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,2}(:[0-9a-fA-F]{1,4}){1,4}|((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:)?(:[0-9a-fA-F]{1,4}){1,5}|((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)((:[0-9a-fA-F]{1,4}){1,6})|:((:[0-9a-fA-F]{1,4}){1,7}|:)|::(ffff(:0{1,4}){0,1}:){0,1}((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]).){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])|([0-9a-fA-F]{1,4}:){1,4}:((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]).){3,3}(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]))\\]|(?:xn--[a-z0-9\\-]{1,59}|(?:(?:[a-z\\u00a1-\\uffff0-9]-*){0,62}[a-z\\u00a1-\\uffff0-9]{1,63}))(?:\\.(?:xn--[a-z0-9\\-]{1,59}|(?:[a-z\\u00a1-\\uffff0-9]-*){0,62}[a-z\\u00a1-\\uffff0-9]{1,63}))*(?:\\.(?:xn--[a-z0-9\\-]{1,59}|(?:[a-z\\u00a1-\\uffff]{2,63})))\\.?)(?::\\d{2,5})?(?:[/?#]\\S*)?$", "i")

const regexLong = new RegExp(
	"^" +
	// Protocol Identifier
	"(?:(?:(?:https?):)\\/\\/)" +
	// HTTP Basic Auth
	"(?:\\S+(?::\\S*)?@)?" +
	"(?:" +
	// IPv4 (excl. Private Addresses)
	"(?!(?:10|127)(?:\\.\\d{1,3}){3})" +
	"(?!(?:169\\.254|192\\.168)(?:\\.\\d{1,3}){2})" +
	"(?!172\\.(?:1[6-9]|2\\d|3[0-1])(?:\\.\\d{1,3}){2})" +
	"(?:[1-9]\\d?|1\\d\\d|2[01]\\d|22[0-3])" +
	"(?:\\.(?:1?\\d{1,2}|2[0-4]\\d|25[0-5])){2}" +
	"(?:\\.(?:[1-9]\\d?|1\\d\\d|2[0-4]\\d|25[0-4]))" +
	"|" +
	// IPv6 (excl. Private Addresses)
	"\\[(" +
	"((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){6,6}[0-9a-fA-F]{1,4}|" +
	"((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,6}:|" +
	"((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,5}:[0-9a-fA-F]{1,4}|" +
	"((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,4}(:[0-9a-fA-F]{1,4}){1,2}|" +
	"((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,3}(:[0-9a-fA-F]{1,4}){1,3}|" +
	"((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:){0,2}(:[0-9a-fA-F]{1,4}){1,4}|" +
	"((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)([0-9a-fA-F]{1,4}:)?(:[0-9a-fA-F]{1,4}){1,5}|" +
	"((([0-9a-eA-E][0-9a-fA-F]{0,3})|([fF]([0-9a-cfA-CF][0-9a-fA-F]{0,2})?)|([fF][eE]([0-7c-fC-F][0-9a-fA-F]?)?)):)((:[0-9a-fA-F]{1,4}){1,6})|" +
	":((:[0-9a-fA-F]{1,4}){1,7}|:)|" +
	"::(ffff(:0{1,4}){0,1}:){0,1}" +
	"((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]).){3,3}" +
	"(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])|" +
	"([0-9a-fA-F]{1,4}:){1,4}:" +
	"((25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9]).){3,3}" +
	"(25[0-5]|(2[0-4]|1{0,1}[0-9]){0,1}[0-9])" +
	")\\]" +
	"|" +
	// Hostname
	"(?:xn--[a-z0-9\\-]{1,59}|(?:(?:[a-z\\u00a1-\\uffff0-9]-*){0,62}[a-z\\u00a1-\\uffff0-9]{1,63}))" +
	// Domain name
	"(?:\\.(?:xn--[a-z0-9\\-]{1,59}|(?:[a-z\\u00a1-\\uffff0-9]-*){0,62}[a-z\\u00a1-\\uffff0-9]{1,63}))*" +
	// TLD
	"(?:\\.(?:xn--[a-z0-9\\-]{1,59}|(?:[a-z\\u00a1-\\uffff]{2,63})))" +
	"\\.?" +
	")" +
	// Port Number
	"(?::\\d{2,5})?" +
	// Pathname
	"(?:[/?#]\\S*)?" +
	"$", "i"
);

TODO: Avoid any form of :: and ::1 within the IPv6 RegEx.

TODO: Support Full and Compressed IPv6 and IPv6v4.