How to multiply field using developer Field Value only

I greatly need your help on how to twist my js code not to use front end input value but only use Field Value from development area for calculation and deliver the usual way on #total
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Twist this as an example for me
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$("#field1,#field2").on("change", function(){
  $("#total").val(parseInt($("#field1").val()) + parseInt($("#field2").val()));
});

Sorry but not sure what it is you mean.

sorry my tag is chronoform v6.I want to use js calculation code but I need it to only use my own input value field value to run the calculation because that field will be disabled for user at front end.

So do it then? Use a hidden field. Just DON'T use that front end calculated value in the backend for obvious reasons.

Healyhatman. I didn't understand you. Can you please share more light on this.
I really need help

Use a hidden field and calculate using the value of that
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Or
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Hard code the value
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Or
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In the js code block use {var:myvalue} and set that var before the page load
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whatever you choose, just don't send that calculated value and use it in your form data because the client could very easily change it before sending. Do your final calculation on the server with a PHP block.