Sparse arrays vs full arrays
JavaScript performance comparison
Preparation code
<script>
Benchmark.prototype.setup = function() {
var n, N, i, I, sparse = [],
full = [],
full2 = [];
N = 16384;
I = 8;
for (i = 0; i < I; i++) {
do {
n = (N * Math.random())  0;
if (n > (N  1)) {
n = N  1;
}
} while (sparse[n]);
sparse[n] = 100 + 200 * Math.random();
}
full.length = N;
full2.length = N;
for (i = 0; i < N; i++) {
if (typeof sparse[i] === "number") {
full[i] = sparse[i];
full2[i] = sparse[i];
} else {
full[i] = 0;
full2[i] = 100 + 200 * Math.random();
}
}
};
</script>
Test runner
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Test  Ops/sec  

Sparse array sum 

pending… 
Full array sum 

pending… 
Running sparse on full array 

pending… 
Sum all elements on a full array without zeros 

pending… 
Sparse array sum (using "forin") 

pending… 
Compare results of other browsers
Revisions
You can edit these tests or add even more tests to this page by appending /edit
to the URL. Here’s a list of current revisions for this page:
 Revision 1: published by Mattias Ernelli
 Revision 3: published
 Revision 6: published by Jasmine
 Revision 7: published
 Revision 8: published by Andreas Öman
 Revision 9: published
 Revision 10: published
 Revision 11: published
 Revision 12: published
 Revision 16: published by Lee Byron
 Revision 19: published
1 comment
Stefan K. commented : ∞
Added a version that uses a forin loop to sum the sparse array, which seems to be much faster in Firefox 21.