This is my the example where user can enter the code between 1 to 100 only otherwise return false.

```js
var regexCode = /var regexEmail = /^0*(?:[1-9][0-9]?|100)$/;

 $(document).on('change','#code',function(){
    if (!regexCode.test($("input#code").val())) {
      alert("Please enter valid code");
      $("input#code").focus();
      return false;
    }
});

```

```html
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>

<input name="code" id="code" placeholder="code" required>
```

Now it accepting digits between 1 to 100 but I need it to accept the code e.g between

`user1` to `user100` only otherwise return false.