High memory usage (11x). about lz-string HOT 2 CLOSED

Almost all of this comes from the way you are building the result string, context_data_string += … lines.

Replacing context_data_string with an Array and doing push/join('') decreases 900M to 80M.
You could also preallocate the Array of some fixed length (depending on the input length) and manually use [i++] on that. I haven't measured which of those the variants (string, Array.prototype.push, preallocated Array) is faster.

from lz-string.

Ok, here are the test results with iojs:

50000 iterations, String concat (current): 31 seconds, 905 MiB.
50000 iterations, Array push/join: 29 seconds, 81 MiB.
50000 iterations, Array prealloc/[i++]/join: 32 seconds, 81 MiB.
50000 iterations, Array push/join + ES6: 15 seconds, 79 MiB.

100000 iterations, String concat (current): 1212 seconds, 1760 MiB, the gc kicked in,
100000 iterations, Array push/join: 57 seconds, 114 MiB.
100000 iterations, Array prealloc/[i++]/join: 69 seconds, 115 MiB.
50000 iterations, Array push/join + ES6: 30 seconds, 107 MiB.

200000 iterations, String concat (current): I terminated it after 100 minutes, 2450 MiB, the gc kicked in,
200000 iterations, Array push/join: 120 seconds, 172 MiB.
200000 iterations, Array prealloc/[i++]/join: 139 seconds, 172 MiB.
50000 iterations, Array push/join + ES6: 61 seconds, 164 MiB.

There is enough free memory and swap is disabled, so it didn't affect the results.

from lz-string.