How to use Javascript Tools? does it has one for each branch?

I use jt cs5 and test a file like pic show, when run, it told document is not define.

what's wrong with it? function is as follow,

function f2c(s) {
  var test = /(\d+(\.\d*)?)F\b/g;    // 初始
  return(s.replace
    (test,
      function($0,$1,$2) {
        return((($1-32) * 5/9) + "C");
      }
    )
  );
}
document.write(f2c("Water freezes at 32F and boils at 212F."));