Perhaps try something like:

function myFunc(obj){
    var param = obj.hasOwnProperty('param') ? obj.param : undefined;
    console.log(param);
}

var funcString = "myFunc({ param: 'something' });",
    Construct = new Function(funcString);

Construct();

Haven't tested it to be honest ... but this way you avoid eval().

more info on Function object

There are multiple ways to achieve this.

Function

Create a Function and set the body:

var dynamicJS = "var x = 1+1  return 2;"
var DoSomething = new Function("value", dynamicJS );

eval()

While arguably less secure¹, eval() can be used.

var dynamicJS = "function DoSomething(value){var x = 1+1  return 2;}"\
eval(dynamicJS);

Caution

Please read this section of the MDN documentation about eval() .

Don't use eval needlessly!

_{eval() is a dangerous function, which executes the code it's passed with the privileges of the caller. If you run eval() with a string that could be affected by a malicious party, you may end up running malicious code on the user's machine with the permissions of your webpage / extension. More importantly, third party code can see the scope in which eval() was invoked, which can lead to possible attacks in ways to which the similar Function is not susceptible.}

_{eval() is also generally slower than the alternatives, since it has to invoke the JS interpreter, while many other constructs are optimized by modern JS engines.}

_{There are safer (and faster!) alternatives to eval() for common use-cases.} ¹

See a demonstration of these methods utilized below.

var dynamicJS = "function DoSomething(value){var x = 1+1;  return 2;}"
var functionBody = "var x = 1+1;  return 2;";
document.addEventListener('DOMContentLoaded', function() {
  document.getElementById('eval').addEventListener('click', function() {
    eval(dynamicJS);
    console.log('DoSomething: ',DoSomething(3));
  });
  document.getElementById('function').addEventListener('click', function() {
    var dynamicFunction = new Function("value", functionBody);
    console.log('dynamic function():',dynamicFunction(3));
  });
});

<button id="eval">click to eval</button>
<button id="function">click to use Function</button>

¹_{https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval#Don't_use_eval_needlessly!}