Declaring a variable higher up the scope chain

Question

I doubt this is possible, but I'd like to give it a shot.

I'd like write a function that introduces new variables into the scope of its caller.

The goal is to do something like this:

(function() {
    var x = {a: 5, b:6};
    console.log(typeof a, typeof b); // prints: undefined undefined
    magicImport(x);
    console.log(a, b); // prints: 5 6
})();

// Variables are not in global scope
console.log(typeof a, typeof b); // prints: undefined undefined

If magicImport(x) does something like

eval("var a = x.a; var b = x.b;");

that doesn't really help, since the scope of a and b will be limited to inside magicImport.

And of course

eval("a = x.a; b = x.b;");

is no good since that will modify the global object.

Is there any way to eval code within a higher scope?

EDIT: The goal, in case it isn't clear, is to create function that can import the contents of a namespace without polluting the global scope, and without necessarily having to place those imported objects into a new container object.

Answer 1

Don't do this. Unless you want to end up in a maintainance nightmare.

If I call a function I want to know what side effects it has, what if the the imported stuff changes? I will break everything. I can hardly imagine any need for such magic driven, unmaintainable code, if you really need to import stuff, return a object and use its properties, but don't do scoping magic, since this won't work with closures or other good features of the language.

Answer 2

I'm not sure if this is what you want, but you could just use the with statement:

function() {
    var x = {a: 5, b:6};
    console.log(typeof a, typeof b); // prints: undefined undefined
    with(x) {
        console.log(a, b); // prints: 5 6
    }
}

Anyway, since this will modify the such called scope chain (pushing all propertys upfront), any other call within a with statement will become slower. This is one reason why it's not recommendable to use it. (deprecated in ES5 ES5 strict-mode anyway)