Javascript regex allow only specific characters

You need to double escape all escape sequences for constructing RegExp object. However better to just use regex literal in your case:

var regex = /^[a-zA-Z0-9 \b\n\r\f\t\v]+$/;

Full code:

$('#p_title').keypress(function (e) {
        var regex = /^[a-zA-Z0-9 \b\n\r\f\t\v]+$/;
        var str = String.fromCharCode(!e.charCode ? e.which : e.charCode);
        if (regex.test(str)) {
           return true;
        }
        e.preventDefault();
        return false;
});

Try use .on instead .keypress:

http://jsfiddle.net/z9wvfj1e/1/

// Filter invalid characters in title
$('#p_title').on('keydown', function (e) {
        if (e.keyCode >=37 && e.keyCode <=40) return true;
        var regex = new RegExp("^[a-zA-Z0-9 \b\n\r\f\t\v]+$");
        var str = String.fromCharCode(!e.charCode ? e.which : e.charCode);
        if (regex.test(str)) {
                console.log(e);
                return true;
        }
        e.preventDefault();
        return false;
});

Something like this sounds like all you need:

$('#p_title').keypress(function (e) {
  return /[a-z]|\s|\r?\n|\t/i.test(String.fromCharCode(e.which));
});

I am doing a case-insensitive check for whether the character entered is a letter OR a space OR a newline OR a tab.

Furthermore, you don't need to check for e.charCode with jQuery because:

The event.which property normalizes event.keyCode and event.charCode. It is recommended to watch event.which for keyboard key input.

https://api.jquery.com/event.which/