Replace unshift where possible for performance improvement

[nosvalds]

Found this when debugging an application I wrote that needs to query some 50-60MB XML files. Using the Chrome Dev tools CPU profiler I identified one of the longest calls was on .unshift(), following some of the suggestions in this post I replaced the unshift calls that I could with .push() and .reverse(). Seemed to make a marked improvement in the CPU profiler report in that area.

Tests are still passing.

CPU Profile Before (17630ms on res.unshift(tokenValue.pop()) ) :

CPU Profile After ( push() and reverse() calls are around ~6200ms, down from 17630ms call to unshift() ) :

[JLRishe]

Hello @nosvalds, I'm sorry that I have left this PR unresponded for so long. I would like to incorporate your change, but it looks like you used your master branch as the source branch for this PR, and other, unrelated changes have since been added to that branch.

I believe I could cherry-pick the relevant changes myself, but I would like you to get credit for the PR if you want it. If so, could you modify the PR to have only the changes in question (if that's possible), or create a new PR?

I'm happy to merge the changes myself if it's a hassle for you.

Thanks again!

[nosvalds]

Hey @JLRishe , sorry I'm not super active on GitHub with my current job. Apologies for using the wrong source branch here and no worries on you going ahead making the changes. I don't mind not getting credit.

Thanks,
Nik