I'm trying to calculate a proportional height (while excluding a static height element) from a width that gets passed in via a request (defaults to 560).

However, `wF.h` evaluates to `NaN`. If I replace `this.w` with 560 it works, but not when trying to reference the `w` property of `wF`.

```
var wF = {
       w : 560,
       h : (312 - 42) / (560 / this.w) + 42
};

```

What gives?

I refuse to use two plain vars in succession, because I'm trying to get nice code out of JS.

**Update:**

Thanks to everyone who helped explain and solve my problem. I guess i'll just have to get used to that. I'll be setting the object up in stages to get on with the project, even though it still annoys me slightly ;). I found and read a nice article on the topic for anyone who stumbles upon similar issues: <http://yehudakatz.com/2011/08/11/understanding-javascript-function-invocation-and-this/>