Question

I have this code…

function a(options) {
    for (var item in options) {
       if ( ! options.hasOwnProperty(item)) {
          continue;
       }
       this[item] = options[item];
    }
}

a({ 'abc': 'def' });

jsFiddle.

Whilst this unpacks variables from the object, it sets them to global scope (attached to window) because this is window in that circumstance.

So after the function I can do alert(abc) and it will alert def, which isn’t good.

How would I set the scope of the variables to the function?

Answer 1

If you want to put the properties of the object in the scope of the function, you can extend the scope by using with:

function a(options) {
    with(options) {
        // properties of `options` are in the scope
        alert(abc);
    }
}

Disclaimer: Make sure you read the documentation and about disadvantages of with. It should be avoided and is also kind of deprecated:

Using with is not recommended, and is forbidden in ECMAScript 5 strict mode. The recommended alternative is to assign the object whose properties you want to access to a temporary variable.

So the questions is why not stick with options ?