JQuery语法错误无法识别的表达式

$("#EMPLOYEE_ALT option:[value='"+$("#EMPLOYEE_ID").val()+"']").remove();

the above code gives the following error:

Uncaught Error: Syntax error, unrecognized expression: #EMPLOYEE_ALT\ option:[value='9999']

9999 is employee id witch is correct and this value suppose to be sent via ajax and return with something.

$.post("url", { emp: $("#EMPLOYEE_ID").val(),ajax: "yes"  },

You have unexpected : in your selector. The correct selector would be

$("#EMPLOYEE_ALT option[value='"+$("#EMPLOYEE_ID").val()+"']").remove();

Try this:

"#EMPLOYEE_ALT option[value='"+$("#EMPLOYEE_ID").val()+"']"

The attribute selector doesn't haves : on it. That is used for CSS's pseudo-classes only.

$("#remove").on("click", function() {
    $("#EMPLOYEE_ALT option[value='9999']").remove();
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<select id="EMPLOYEE_ALT">
  <option value="1">1</option>
  <option value="9999">9999</option>
</select>

<button id="remove">Remove item '9999'</button>

</div>