JavaScript verifies that users enter characters, numbers, and ASCII charts.

We can judge characters or numbers based on the event. keyCode of the onkeydown event, that is, ASCII Chart. ASCII code corresponding to the relevant keyboard key:
 
Refer to the following JavaScript code:
Copy codeThe Code is as follows:
<Script type = "text/javascript">
Function isNumeric (keyCode)
{
Return (keyCode> = 48 & keyCode <= 57) | keyCode = 8)
}
</Script>
<Script type = "text/javascript">
Function isAlpha (keyCode)
{
Return (keyCode> = 65 & keyCode <= 90) | keyCode = 8)
}
</Script>
<Script type = "text/javascript">
Function isAlphaOrNumeric (keyCode)
{
Return (keyCode >=48 & keyCode <= 57) | (keyCode >=65 & keyCode <= 90) | keyCode = 8)
}
</Script>

In this example, you can only enter characters and numbers, and use the onpaste event.
Copy codeThe Code is as follows:
<Asp: TextBox ID = "TextBox1" runat = "server" onkeydown = "return isAlphaOrNumeric (event. keyCode);" onpaste = "return false;"> </asp: TextBox>