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Comment by jarin | Hacker News Reader

From the comments:

"As for your question, we pass in `document` that way to prevent unnecessary scope lookups. We could’ve used `var d = document` inside the IIFE, but that would trigger an additional scope lookup. For `'script'` it doesn’t matter; you could initialize that inside of the IIFE if you want."

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It's premature optimization. The extra time taken for a scope lookup is completely insignificant compared to the network costs in loading the script.

Perhaps if this was inside a tight inner loop, I could understand, but here it's completely unneccessary.

Sure, but what's the drawback? I think very simple premature optimizations are just fine, especially when someone else does them for me.

It looks like the kind of optimization that a compiler could do pretty trivially, and you shouldn't have to be concerned about as a human, as it makes the code less readable.

Then again, Javascript is a strange animal here as the code is provided to the execution environment as plaintext instead of bytecode/assembly. I guess a JS-to-JS compiler such as closure could handle it.

Is it premature or unnecessary, if the methodology comes natural? Why not get into the habit of reading and writing Javascript with optimization naturally ingrained into the first pass? The optimization(s) may not be immediately necessary here, but there's no harm in practicing these patterns in all facets of language use, unless we want to have a separate conversation whether the patterns are detrimental to syntax.

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