<script>
var x = "x";

for (var i = 1; i < 23; ++i) {
    x = x + x;
}

// x should now be a 2^23 character string, which is 16M in size.

var y;

// now append to it repeatedly in a way that prevents buffer sharing
for (var i = 0; i < 1000; ++i) {
    y = x + i;
}    
</script>