Convert string to variable name in Javascript

Javascript has an Eval() function for such occassions

function (varString) {
  var myVar = eval(varString);
  // .....
}

Edit: Sorry, I think I skimmed the question too quickly. This will only get you the variable, to set it you need

function SetTo5(varString) {
  var newValue = 5;
  eval(varString + " = " + newValue);
}

But I imagine there is a more appropriate way to accomplish what you're looking for? I don't think eval() is something you really want to use unless there's a great reason for it. eval()

You can access the window object as an associative array and set it that way

window["onlyVideo"] = "TEST";
document.write(onlyVideo);

var myString = "echoHello";

window[myString] = function() {
    alert("Hello!");
}

echoHello();

Say no to the evil eval. Example here: http://fiddle.jshell.net/Shaz/WmA8t/

As far as eval vs. global variable solutions...

I think there are advantages to each but this is really a false dichotomy. If you are paranoid of the global namespace just create a temporary namespace & use the same technique.

var tempNamespace = {};
var myString = "myVarProperty";

tempNamespace[myString] = 5;

Pretty sure you could then access as tempNamespace.myVarProperty (now 5), avoiding using window for storage. (The string could also be put directly into the brackets)