js 变量做方法名的方法--都可用

<script>
function a(e){alert(e);}
function b(e){alert(e);}
function aa(){
 var txt = 'a';
 var txt2='2315';
 eval(txt+"('"+txt2+"');")
}
aa();

</script>

function dynamicInvocationMethod(mehodName, params) {
        return eval(mehodName)(params);
    }
function  method_1(lyrics) {
       if (lyrics == null) {//arguments.length == 0  
           return("la la la!");
       } else {
           return(lyrics);
       }
   }  


alert(dynamicInvocationMethod("method_1", "my name is tom"));