Dynamically Forming a JSON object traversion without using eval.

Question

Given I have the following: (which is dynamically generated and varies in length)

associations = ["employer", "address"];

Trying to traverse the JSON object, and wanting to form something like the following:

data.employer.address

or

data[associations[0]][association[1]]

Without doing this:

eval("data."+associations.join('.'));

Finally, I may be shunned for saying this, but is it okay to use eval in an instance like this? Just retrieving data.

Answer 1

Why not just iterate over your associations?

function traverse(data, associations){
  for (var i=0; i<associations.length; i++){
      data = data[associations[i]];
  }
  return data;
}

Your eval method has to generate a new string and parse the code before it can even start traversing.

Answer 2

Here’s one way using Prototype.

$A(associations).inject(data, function (obj, method) {
  return obj[method];
});

Using eval is fine if you can guarantee the user won’t be able affect the string you’re passing to it. If your input is coming from the user or from a URL that could be changed by the user, you should probably avoid eval.

Answer 3

You can always create a dynamic script node. For instance:

var yo = document.createElement("script");
yo.setAttribute("type", "text/javascript");
yo.innerHTML = "alert('yo!');";
document.body.appendChild(yo);

No eval required.