Javascript shield keyboard retains the last two decimal places

<Script language = "JavaScript">

Function check (thetext)
{
Alert (window. event. keycode );
}
Function btnclick ()
{
Alert (event. srcelement. type); // button
Alert (event.Srcelement. Tagname); // Input
Alert (event. srcelement. ID); // BTN
Alert (event. srcelement. Name); // BTN
Alert (event. srcelement. Value); // OK
}

// Control the input in the form of a value
Function checknum (thetxtnum)
{
VaR _ value = thetxtnum. value;
VaR kc = Window. event. keycode;

If (Kc = 110 | kc = 190) // If yes.
{
If (_ value. Length = 0) // The first input is not allowed.
{
Alert ("cannot begin with a decimal point! ");
Window. event. returnvalue = false;
Return;
}
If (_ value. indexof (".")> = 0) // if it already exists.
{
// Window. event. keycode = 8;
Alert ("the decimal point cannot be entered again! ");
Window. event. returnvalue = false;
Return;
}
}

// Alert (KC );
If (KC> = 48 & kc <= 57) | (KC> = 96 & kc <= 105) | kc = 110 | kc = 190) // if it is a number or.
{
Window. event. returnvalue = true;
Return;
}
Else if (Kc = 8) // if it is a backspace
{
Thetxtnum. Select ();
Thetxtnum. value = "";
Thetxtnum. Focus ();
Window. event. returnvalue = false;
Return;
}
Else if (Kc = 13)
{
Window. event. keycode = 9;
Window. event. returnvalue = true;
Return;
}
Else if (Kc = 9 | kc = 45 | kc = 46 | kc = 16 | kc = 17 | kc = 18 | KC = 20 | (KC> = 112 & kc <= 123 ))
{
Window. event. returnvalue = true;
Return;
}
Else
{
// Window. event. keycode = 8;
Alert ("enter a number! ");
Window. event. returnvalue = false;
Return;
}
}

// Retain the last two decimal places
Function transfer (thetxtnum)
{
VaR _ value = parsefloat (thetxtnum. value );
If (isnan (_ value ))
{
Return;
}
Thetxtnum. value = _ value. Tofixed(2 );
}

</SCRIPT>

<Input type = text id = "TXT" name = "TXT" onkeydown = "check (this)"/>

<Input type = "button" id = "BTN" name = "BTN" value = "OK" onclick = "btnclick ()"/>

<Br/>

value: