.Net Interview Questions, Resources, Tips & Tricks.

In order to allow user to enter only certain characters in a textbox and also to control the maximum length of multiline textbox use the below function by calling it on onkeypress for a textbox.

And also to handle the cases where the user copy paste the content containing the invalid characters first we will prepare the regular expression to and check for invalid characters and replace with empty (remove invalid characters from pasted content).

Then we will get the pressed key and check the key pressed by user while entering the text into a textbox and check if it is in part of valid character and based on which we will stop user from entering invalid characters.

One important thing here is we need to allow few keys like backspace, Arrow keys, Home, End etc.. for that we will make sure that the key pressed is not in (27, 9, 32, 8, 36, 37, 35, 13, 0).

function ValidateName(name,e)
{
        var nameRegex = /^[A-Za-z',.-]{0,50}$/;
        while (!name.value.match(nameRegex)) 
        {
            name.value = name.value.replace(/[^a-zA-Z,'.-]+/, "");
        }
        e = e || window.event;
        var allow = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ.,'-";
        var allowKeys = new Array(27, 9, 32, 8, 36, 37, 35, 13, 0);
        var keycode = e.which || e.keyCode;
        if (allow.indexOf(String.fromCharCode(keycode)) < 0)
        {
             for (var i = 0; i < allowKeys.length; i++)
             {
                 if (allowKeys[i] == keycode)
                 {
                       return true;
                  }
              }
              return false;
          }
       return true;
    }

Call this function in onkeypress event as shown below.

Onkeypress = "return ValidateName(this,event)"