How to change array variable name dynamically

I am working for some common method in javascript, for that i have to call array dynamically.

 var ddlText, ddlValue, ddl, lblMesg, ddlTextCacheList_Designation, ddlValueCacheList_Designation, ddlTextCacheList_Scale, ddlValueCacheList_Scale;
 function cacheDes() {

        var listDes = document.getElementById("<%=List_Designation.ClientID %>");
        ddlTextCacheList_Designation = new Array();
        ddlValueCacheList_Designation = new Array();
        for (var i = 0; i < listDes.options.length; i++) {
            ddlTextCacheList_Designation[ddlTextCacheList_Designation.length] = listDes.options[i].text;
            ddlValueCacheList_Designation[ddlValueCacheList_Designation.length] = listDes.options[i].value;

        }


    }


    function cacheScale() {
        var listScale = document.getElementById("<%=List_Scale.ClientID %>");
        ddlTextCacheList_Scale = new Array();
        ddlValueCacheList_Scale = new Array();
        for (var i = 0; i < listScale.options.length; i++) {
            ddlTextCacheList_Scale[ddlTextCacheList_Scale.length] = listScale.options[i].text;
            ddlValueCacheList_Scale[ddlValueCacheList_Scale.length] = listScale.options[i].value;

        }


    }

    window.onload = function () {
        cacheDes();
        cacheScale();
    };

I want to call array ddlTextCacheList_Scale or ddlTextCacheList_Designation for same method as we know 'ddlTextCacheList_' is common only we need to put 'Scale' or 'Designation' dynamicaaly by passing parameter.

Add:

I get some errors: