Prevent user to type numbers and symbols. However problem something use Capslock Buttons

Question

When I click the input and hit Caps Lock, Backspace, it sends the patch message. for example, I type the normal and safe Backspace input to delete everything, when it comes at the end it shows the "fill only with letters" message. I used this code (name.match(/ [a-z" "A-Z_]+$/) but would like to release Capslock and Backspace.

//Reservation validation
const nameinput = document.getElementsByClassName('names');  
const emailinput = document.querySelector('input[name="email"]');  
const submitinput = document.querySelector('input[name="submitreservation"]');  
console.log(nameinput);  
Array.from(nameinput).forEach(function (item) {
item.addEventListener('keyup', function (e) {
var name = e.target.value;

    if (name.match(/^[a-z" "A-Z_]+$/)) {
        e.target.value = name.toUpperCase();
    }
    else {
        console.log(e.target.value)
        alert('Digite apenas letras !');
        e.target.value ="";
    }

})
})