function assert(value, desc) {
var res = $("#results");
var li = document.createElement("li");
li.className = value ? "pass" : "fail";
li.appendChild(document.createTextNode(desc));
res.append(li);
}
// eval executes the code passed to it as string
// it executes in the context in which it is called
// returns the value of the last executed statement
assert(eval("10+20") === 30, "value returned from eval was 30");
assert(eval("var abc = 5;") === undefined, "value returned was undefined because it was just an assignment");
assert(abc === 5, "last statement was executed so abc was created");
assert(eval("cde = 6;") === 6, "however when added to global context, the assigned value is returned");
assert(window.cde === 6, "cde was added in the global scope");
assert(eval("1+1;2+2;") === 4, "returns the value of last executed statement");
//anything complex being used in eval needs to be wrapped up in parentheses
//literal object
var litObj = eval("({description:'this is literal object'})");
assert(litObj !== undefined && litObj.description === "this is literal object", "lit object got created with correct property");
// function object
var fn = eval("(function(){return 'this is function object';})");
assert(fn !== undefined && typeof fn === "function" && fn() === "this is function object", "function object got created");
<div id="results" />
body {margin:10px;}
.pass {color:green;}
.fail {color:red;text-decoration:line-through;}