merging 3 arrays, max of 9

var index = 0;
    results = [],
    prevLen;

while(true) {
  r.albums[index] && results.push(r.albums[index]);
  r.tracks[index] && results.push(r.tracks[index]);
  r.artists[index] && results.push(r.artists[index]);

  if(prevLen == results.length || results.length >= 9) {
    break;
  }
  prevLen = results.length;
  index++;
}
results = results.splice(0,9)

I do love Arthur's code. It's very nice. That said, I'm sort of okay with the "r.albums[index]" test failing, since we are dealing with strings here (albums, artists, tracks), I don't want those falsy values in my array anyway. Kaare's second iteration for(var i = 0; i < max || results.length <= 9; i++) will keep results from getting too large or too slow.

Sorry, should be: for(var i = 0; i < max && results.length <= 9; i++). Arthur was correct.

just for shits n giggles, the C++03 version. Inline initialization of variable size arrays is a bit kludgey, a shortfall which is remedied in C++0x, whose new move semantics would also make the vector copy on return a move operation, i.e. "free." Boost also makes things more concise but I went for the basic version here.
Tested in Xcode 4.

using std::vector;
vector<int> merge3() {
    int src_a[3][4] = { { 1,2 }, { 3,4,5 }, { 6,7,8,9 } };
    vector<int> const va[3] = { vector<int>(src_a[0], src_a[0]+2), vector<int>(src_a[1], src_a[1]+3), vector<int>(src_a[2], src_a[2]+4) };
    vector<int> results;
    int rmax = std::min(9, va[0].size() + va[1].size() + va[2].size());

    for(int rx = 0; results.size() < rmax; ++rx) {
        vector<int> const &vsrc = va[rx % 3];
        int ex = rx / 3;
        if(vsrc.size() > ex) results.push_back(vsrc[ex]);
    }
    return results;
}

C++0x version, not completely sure about correctness, but just to show use of initializer lists, auto typing and move semantics, renamed vars for better comparison with js version, and really, save for a few parentheses and types it's the same. I'm likely the only one of us who cares about this ;)

using std::vector;
vector<int>&& merge3() {
    vector<int> const src_a[3] = { { 1,2 }, { 3,4,5 }, { 6,7,8,9 } };
    vector<int> out;
    int rmax = std::min(9, src_a[0].size() + src_a[1].size() + src_a[2].size());

    for(int rx = 0; out.size() < rmax; ++rx) {
        auto src = src_a[rx % 3];
        int ex = rx / 3;
        if(src.size() > ex) out.push_back(src[ex]);
    }
    return results;
}