var fun1 = new Function("a", "b", "alert(a);")
fun1(1, 2);
这种方式用的及其的少

var fun2 = function(a,b){
	document.write("Result is (sum) :" + (a+b))
}
fun2(2,3);

function fun3(a,b){
	console.log("Result is (sum) :" + (a+b));
}
fun3(3,4);