How to make custom validation error message?

Question

How can I make this kind of error message? I am building a login validation form.

Answer 1

You may try this as simple as it

<input type= "text" name= "name" pattern= "[0-9]" required="required">

You can also set Length

Answer 2

In addition:

You can use customValidity api to create custom messages and will use the default tooltip provided by the browser.

DOCS: https://developer.mozilla.org/en-US/docs/Web/API/ValidityState

Check bellow a simple example:

https://jsbin.com/popazajawu/2/edit?html,js,console,output

JS:

var inputs = document.querySelectorAll('input');

inputs.forEach(input => {
  input.addEventListener('invalid', function(e) {
    e.target.setCustomValidity("[CUSTOM MESSAGE] This field cannot be left blank")
  })

  input.addEventListener('input', function(e) {
    e.target.setCustomValidity("");
  })
})