What is wrong with following event ajax call ffrom form on chanhe od date field

There's a syntax error in the way you are passing the server-side expression. The evaluateServerSideExpression() function expects a string as it second parameter, however, if you need to get values from the form to be passed as parameters of the server-side expression you need to properly build your string. Right now you are literally passing the phrase: FormAPI.getValue("date1").id instead of the actual value of field. The reason is you made this statment part of the string instead of concatenating it to it. You also have a ] at the end which shouldn't be there.

Here's the right version of your expression. I tested it and works as expected:

FormAPI.evaluateServerSideExpression(function(e){window.FormAPI.setValue("number41",e);},"=calworkdays(" + FormAPI.getValue("date1").id + "," + FormAPI.getValue("date2").id +")");

There's a syntax error in the way you are passing the server-side expression. The evaluateServerSideExpression() function expects a string as it second parameter, however, if you need to get values from the form to be passed as parameters of the server-side expression you need to properly build your string. Right now you are literally passing the phrase: FormAPI.getValue("date1").id instead of the actual value of field. The reason is you made this statment part of the string instead of concatenating it to it. You also have a ] at the end which shouldn't be there.

Here's the right version of your expression. I tested it and works as expected:

FormAPI.evaluateServerSideExpression(function(e){window.FormAPI.setValue("number41",e);},"=calworkdays(" + FormAPI.getValue("date1").id + "," + FormAPI.getValue("date2").id +")");