JS URL regex, allow only urls and empty string

Question

I have the following regext:

var regex = /^(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/g;

function test() {
    alert(regex.test(document.getElementById("myinput").value));
}

I want to allow url or empty string. regex solution please
How do I allow empty in this case?
https://jsfiddle.net/6kptovwc/2/
Thanks

Answer 1

Add an alternation with empty string (I've simplified a bit your regex):

^((?:https?:\/\/)?(?:www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b[-a-zA-Z0-9@:%_\+.~#?&\/=]*|)$

or

^((?:https?:\/\/)?(?:www\.)?[-\w@:%.+~#=]{2,256}\.[a-z]{2,6}\b[-\w@:%+.~#?&\/=]*|)$

Demo & explanation

Answer 2

Just add OR(||) condition

function test() {
    const elm = document.getElementById("myinput")
    alert(elm.value === '' || regex.test(elm.value));
}

Answer 3

^$|pattern

var regex = /^$|(http(s)?:\/\/.)?(www\.)?[-a-zA-Z0-9@:%._\+~#=]{2,256}\.[a-z]{2,6}\b([-a-zA-Z0-9@:%_\+.~#?&//=]*)/g;