How to Validate Name and Address using Javascript.

I want user to enter only characters ( a-z) in this textbox.. Spaces are allowed.
<asp:TextBox ID="txtName" runat="server" ></asp:TextBox>

Here, User "should" enter both Characters (a-z) and numbers.. Spaces are also allowed. 
<asp:TextBox ID="txtAddress" runat="server" ></asp:TextBox>
<div>Please can someone show me how to Validate in a simple way? </div> <div>Thanks in advance.</div>

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