avoid deepening the javascript stack

gistfile1.js

// the biggest problem i've faced in "big" js apps (one-page RIAs, mobile and web)
// is the javascript stack.  avoid diving deep as much as possible.  basically
// a function that calls a function that calls a function within a loop is a
// really really bad idea.  especially on mobile devices that typically don't have
// a stack limit as big as a normal browser.

var books = [
  { name: "A", chapters: [ { name: "X" }, { name: "Y" }, { name: "Z" } ] },
  { name: "B", chapters: [ { name: "X" }, { name: "Y" }, { name: "Z" } ] },
  { name: "C", chapters: [ { name: "X" }, { name: "Y" }, { name: "Z" } ] },
  { name: "D", chapters: [ { name: "X" }, { name: "Y" }, { name: "Z" } ] },
  { name: "E", chapters: [ { name: "X" }, { name: "Y" }, { name: "Z" } ] }
];

doSomethingWithBookAndChapter = function (book_name, chapter_name) {
  console.log(book_name, chapter_name);
};

// this isnt the best example, because forEach is native.  things get much worse
// with non-native each() and map() functions found in various libraries.  but
// even so, forEach still increases the stack depth
books.forEach(function (book) {                                      // 1 call, top level of stack
  book.chapters.forEach(function (chapter) {                         // 5 calls (each book), 1 level deep in stack
    doSomethingWithBookAndChapter(book.name, chapter.name);          // 15 calls (3 chapters per book), 2 levels deep in stack
  });
});

// same thing, uglier code, but does not increase the stack
var book, chapters, chapter, bi, bl, ci, cl;
for (bi = 1, bl = books.legth; bi < bl; bi++) {
  book = books[bi];
  chapters = book.chapters;
  for (ci = 1, cl = chapters.legth; ci < cl; ci++) {
    chapter = chapters[ci];
    doSomethingWithBookAndChapter(book.name, chapter.name);          // 15 calls, top level of stack
  }
}

// same thing again, in coffeescript, compiles pretty much to the bare-metal example directly above
for book in books
  for chapter in book.chapters
    doSomethingWithBookAndChapter(book.name, chapter.name)

// now you see why i like coffeescript so much :)