function WriteToFile(passForm) {
set fso = CreateObject("Scripting.FileSystemObject");
set s = fso.CreateTextFile("<your Path>/filename.txt", True);
var firstName = document.getElementById('FirstName');
var lastName = document.getElementById('lastName');
s.writeline("First Name :" + FirstName);
s.writeline("Last Name :" + lastName);
s.writeline("-----------------------------");
s.Close();
}
// HTML
<form onSubmit="WriteToFile(this)">
<label>Type your first name:</label>
<input type="text" name="FirstName" id="firstName" size="20">
<label>Type your last name: </abel>
<input type="text" name="LastName" id="lastName" size="20">
<input type="submit" value="submit">
</form>