Analysis of two cases of using EL expressions in javascript to obtain parameters passed in the background

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The problem I encountered in the project today was that the jsp page referenced a separate js file, but some parameters passed in the background directly used EL expressions to obtain errors in the js file. I searched for information online and found a solution. Make a summary for reference.

There are two situations when using EL expressions in JS to obtain parameters passed in the background.
The first situation:
(1)Introduce the jstl tag library into the jsp page:

   <%@ taglib uri=”http://java.sun.com/jsp/jstl/core” prefix=”c”%>

(2) Write js code on the jsp page:

<script>
    var merchantId=” ${sessionScope.merchantIdMap}”
 </script>

Second case :
(1) Introduce jstl tags into the jsp page Library:

   <%@ taglib uri=”http://java.sun.com/jsp/jstl/core” prefix=”c”%>

(2) The jsp file introduces a separate js file. At this time, EL expressions cannot be used directly in the js file, and an error will be reported. There are two processing methods here:
The first:
Use hidden fields to store parameter values ​​in jsp pages:

<input type=”hidden” id=merchantIdMap” value=”${sessionScope.merchantIdMap}”>

Get the value of this hidden field in js files:

var merchantId=$(“#merhantIdMap”);

Second option:
Define global variables in the jsp page:

<c:set var="merchantIdMapGlob" value="${sessionScope.merchantIdMap}" scope="application"/>
<c:set var="warehouseIdMapGlob" value="${sessionScope.warehouseIdMap}" scope="application"/>
<script>
    var merchantIdMapGlob = "${merchantIdMapGlob}";    
    var warehouseIdMapGlob = "${warehouseIdMapGlob}";
</script>

You can use this global variable directly in the js file:

var merchantId = merchantIdMapGlob;

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