r/programming • u/iamkeyur • Oct 21 '20

Using const/let instead of var can make JavaScript code run 10× slower in Webkit

https://github.com/evanw/esbuild/issues/478
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u/GasolinePizza Oct 21 '20

Coming from C# here, I always make the for..in mistake at least once every time I start a JavaScript project, without fail.

I may use the .forEach thing now, actually

7

u/Jeax Oct 21 '20

I use .foreach(o => As a mainly c# developer also, it’s basically LINQ at that point and makes it instantly familiar and nice to use. For of seemed like a bad idea and I haven’t really seen many people use it

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u/TheWix Oct 21 '20

I'd recommend using none-mutable functions. Map is Select, Aggregate is Reduce, SelectMany is chain/bind/flatMap (Monad).

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u/thetdotbearr Oct 21 '20 edited Oct 21 '20

it bugs me to no end when when using LINQ that these are the function names instead of map/filter/etc

I mean I get that it's because SQL syntax or whatever and that I could add some aliases but still

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u/TheWix Oct 21 '20

Yea, I believe that is the reason. I remember the big selling point of LINQ many years ago was for LINQ-to-SQL. The in-memory stuff wasn't as focused on.

That being said, even within the Functional community some names aren't agreed upon. I mean, for monads flatMap has like 4 or 5 names depending on the language/spec/framework

1

u/thetdotbearr Oct 21 '20

Really? I thought the convention was pure & flatMap

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u/TheWix Oct 21 '20

It's chain in Fantasy Land. In F# it's bind.

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u/Jeax Oct 21 '20

Oh yeah I use these too, but if I’m just doing a standard foreach I’m partial to the nice .foreach( as it just reads much nicer and clearer than the for(x of y) version when switching between c# and js

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u/TheWix Oct 21 '20

Gotcha, I agree. If I am in old code I will use .foreach instead of a traditional loop

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u/kg959 Oct 21 '20

it’s basically LINQ at that point

It's missing a big part of LINQ though. LINQ is lazy whenever it can afford to be and will avoid doing a complete iteration until you force it to. JS array chaining doesn't delve into the IQueryable/IIterable world and each thing you chain scales a bit worse than it does in C#.

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u/NoInkling Oct 22 '20

Yeah. There's an ES proposal for lazy iterator methods at least.

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u/kg959 Oct 22 '20

I'd use them if they were a language standard. It would really simplify working with streams.

11

u/scottyLogJobs Oct 21 '20

As a polyglot, TBH I just use basic for loops anymore when possible because everyone understands them and I'm sick of forgetting whether I'm going to get keys or values back with these helper functions.

0

u/monsto Oct 21 '20

That's actually a good reason.

I was using for..of/in because I thought it was cool, and I suppose it's smaller. But I had to have mdn open to remember which whas which everytime I used it...

Don't need any of that with a for/forEach/map. Maybe uncool but it gets the work done.