js用eval出错

Question

总是提示 return 时result 未定义  可明明定义了
<script language="JavaScript">
var bolaa_cpm_agmtid = "3f022" ;
eval("var bolaa_cpm_agmtid"+bolaa_cpm_agmtid+"='ff';");
var domains=unescape("%u0062%u006F%u006C%u0061%u0061%u002E%u0063%u006F%u006D");
alert("数据"+isRepeatAd("test"));
function isRepeatAd(aaa){// check is repeat ad
    alert("执行函数"+aaa);
var bolaa_cpm_cmd;
alert(bolaa_cpm_cmd);
bolaa_cpm_cmd +="var result = true;";
    bolaa_cpm_cmd="  var bolaa_cpm_agmtid"+bolaa_cpm_agmtid+";";//
bolaa_cpm_cmd +=" if (bolaa_cpm_agmtid"+bolaa_cpm_agmtid+" == null || bolaa_cpm_agmtid"+bolaa_cpm_agmtid+" == 'undefined') {";
bolaa_cpm_cmd +=" bolaa_cpm_agmtid"+bolaa_cpm_agmtid+" = 'loadok';";
//bolaa_cpm_cmd +=" result = false;";
bolaa_cpm_cmd +=" } ";
alert(bolaa_cpm_cmd);
eval(bolaa_cpm_cmd);
return result;
}

Answer 1

bolaa_cpm_cmd="     var   bolaa_cpm_agmtid"+bolaa_cpm_agmtid+";";// 
-------------^此处应为+=

Answer 2

var   bolaa_cpm_cmd;
alert(bolaa_cpm_cmd);
bolaa_cpm_cmd   ="var   result   =   true;"; // 这里不要用bolaa_cpm_cmd   +=
        //bolaa_cpm_cmd="     var   bolaa_cpm_agmtid"+bolaa_cpm_agmtid+";";// 这里不要用bolaa_cpm_cmd= eval(bolaa_cpm_cmd);
alert(result);

Answer 3

bolaa_cpm_cmd   +="var   result   =   true;";
把双引号去掉