Question

I have an object in my class like so:

this.options = {
     a: 1,
     b: 2,
     ...
};

I just wondered if there was a way to “attach” the options object to the current scope in Javascript, such that I can refer to a and b directly (instead of this.options.a and this.options.b). Something like:

attach(this.options);
var myVariable = a + 3; // 4
detach(this.options);

or

with( this.options, {
   // code here
 var myVariable = a + 3; // 4
});

In the above, the attach and with have the effect of taking all of the children of this.options and attaching them to the current scope so they are accessible via a instead of this.options.a. (The with version simply detaches this.options once you’re done, enclosing the potentially-damaging attaching to within that scope).

As long as it works in the Spidermonkey/Mozilla engine, I don’t mind if it’s not portable.

I only mention this because of curiosity & laziness: all the nested names are getting annoying to type out, and I know that in the R language this is possible (in fact, the syntax in the snippets above is almost exactly what you’d write in R to achieve this).

Answer 1

JavaScript has a with statement that works similar to what you describe:

with (this.options) {
    var myVariable = a + 3;  // here a is actually this.options.a
}

However as you can see at the MDN article I linked to there are some cons to using it, because, e.g., of potential ambiguity. In the example above, a could be a property of this.options, or it could be a variable defined elsewhere, and looking just at that block there is no way to tell.

with is not recommended (and is forbidden in strict mode).

There is a safe alternative though: create a variable that references (again in your example) this.options:

var o = this.options;

var myVariable = o.a + 3;

It’s not quite as short as typing a on its own, but it’s shorter than repeating this.options everywhere.