Cannot make regex working on HTML pattern attribute

Question

My regex works fine on regex101 and my regex is

[1-4]|(0)

But when I tried it on HTML input element's attribute it doesn't work as expected. My HTML is like below

<form action="/">
     <input type="text" id="usernum" name="usernum" pattern="[1-4]|(0)" title="1-4 and must include at leat one 0">
     <input type="submit">
</form>

I want users must enter one 0 along with the ranges digit.

| is for alternatives. So that matches either 1 through 4 or 0. It's the same as [0-4]. — Barmar
– Barmar, Commented Jun 17, 2020 at 5:28
If i use [0-4] user can skip 0 but I want to force them to enter at least one 0 — Delowar Hossain
– Delowar Hossain, Commented Jun 17, 2020 at 5:31
I know. I'm just explaining what your code does. Why did you think |0 would force a 0? — Barmar
– Barmar, Commented Jun 17, 2020 at 5:36

Barmar · Accepted Answer · 2020-06-17 05:35:10Z

1

The pattern attribute has to match the entire input.

([1-4]+0[0-4]*|[0-4]*0[1-4]+)+

The first alternative requires at least one digit 1-4 before a 0, the second requires at least one digit 1-4 after a 0. Then repeat it with + to allow more than one 0.

DEMO

answered Jun 17, 2020 at 5:35

Barmar

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