HTML form validation for number

I don't think there is a simple regex for a range between 0001 and 9999.

^(0{3}[1-9]|0{2}[1-9]\d|0[1-9]\d{2}|[1-9]\d{3})$

My solution is to split expression for each degree.

0{3}[1-9]   = 0001 - 0009
0{2}[1-9]\d = 0010 - 0099
0[1-9]\d{2} = 0100 - 0999
[1-9]\d{3}  = 1000 - 9999

You can play with this regex online https://regex101.com/r/TjzoEh/1

Use pattern attribute of text input to validate your regex.

<input type="text" pattern="^(0{3}[1-9]|0{2}[1-9]\d|0[1-9]\d{2}|[1-9]\d{3})$" title="Four digits code">

Inspired by https://www.regular-expressions.info/numericranges.html

for set your length, you must use maxlength attribute like this:

<input type="text" maxlength="4"/>

and for check number type, you can use Regular Expressions or Number.isInteger() method.

For first way, you can use this pattern and find any non-digit in your input

// Find a non-digit character
let reg = /\D/;

and finally, use it:

reg.test({{your value}})

For second way, you have to use eval() method in the Number.isInteger() method, for example:

Number.isInteger(eval({{ your value }}))

NOTE: if you use type="number" attribute in input, use don't have to use regex or any js methods.