isType performance enhancements #2886
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In Node.js 10 on a 2012 Mac Mini, this reduces the time of a single call to _.isString and similar functions from 192 ns to 63 ns.
After optimizing the internal tagTester function, I decided to re- evaluate the optimization and benchmark discussed from jashkenas#2840 (comment) onwards. Now that tagTester is faster, the tradeoff posed by this optimization had become less obviously in favor. Especially evaluating the length of strings appeared to be relatively costly. I realized this was happening twice, so I removed the redundant evaluation. This could be done at a net zero weight change.
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After completing #2884 and while working on #2878, I realized that I might have somewhat pessimized path evaluation by calling
_.isArraymore often through_.toPath. Coincidentally, I also noticed that the internaltagTesterwas needlessly recomputing the[object Type]tag on every invocation. Since the isType functions are used everywhere, I decided to offset the_.toPathpessimization with an optimization across the board.I then revisited the benchmarks discussed from #2840 (comment) onwards, because I suspected the tradeoff for the optimization in
_.isEmptymight have changed. Indeed, it had;_.isEmpty({})still took about three times as much time without the optimization than with it, but in Node.js,_.isEmpty('')took five times as much time with the optimization than without it. I was then able to establish a good compromise between the optimized and the unoptimized performance profiles, by making the optimization itself more efficient. This evaluatesobj.lengthonly once instead of twice, which keeps the intended effect of the optimization while also avoiding the performance penalty for strings in Node.js.This PR is just to leave a trace. The weight does not change significantly and performance is likely to improve for applications that call isType functions inside hot loops. If the CI checks pass, I'll merge this without waiting for a review. Nevertheless, a review by a spontaneous volunteer is still welcome.