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Optimize for readability above everything else. Almost all of these examples I'd argue would be better suited for something like .map(). Little point in being o

Optimize for readability above everything else. Almost all of these examples I'd argue would be better suited for something like .map(). Little point in being overly cute, and if you are working with arrays large enough such that doing multiple passes is that much of a performance hit client-side, you have other issues going on.

jrimbault 7y ago
That's also my minor nitpick, I feel like the syntax : `list.filter(myFilter).map(transform)` is clear about what I do and, each functions has a clear goal. Otherwise I enjoyed reading this.
- mikeryan 7y ago
  While your example reads a bit better, you’re now iterating through your list twice.
  - fwip 7y ago
    Most code isn't performance-critical. This pattern will probably be dominated by the time taken to filter and map, not loop iteration.
  - londt8 7y ago
    Technically there is no iteration in filter/map/reduce at all.
    - Stratoscope 7y ago
      That's incorrect. All of those functions are implemented using iteration. Consider this excerpt from the .map() polyfill on MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map#Polyfill https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... // 7. Let k be 0 k = 0; // 8. Repeat, while k < len while (k < len) { // [loop body omitted] // d. Increase k by 1. k++; }
  - saagarjha 7y ago
    Does JavaScript have adapters to covert lists into generators or lazy iterators?
    - hn_throwaway_99 7y ago
      Unfortunately not in a way that can optimize these methods. This is one reason the Java Streams API, which has a similar purpose (e.g. map, filter, flatMap, reduce, etc.), is a better design IMO because you can chain together method calls without creating (and iterating) the full array at each step.
_bxg1 7y ago
I think the intent was simply to teach. Obviously if something can be done with map() instead of reduce(), it'll be more readable as map(). But seeing how the other list functions can be made out of reduce() helps you understand how it works.
azangru 7y ago
> Almost all of these examples I'd argue would be better suited for something like .map() Roughly half of his examples take an array and return either a differently-sized array, or a different data structure altogether. I can’t imagine how one could argue for a map in these cases.
- noir_lord 7y ago
  Indeed, reduce is the swiss army knife since you can use it (sometimes when you shouldn't) to implement most of the other methods of map/filter etc.
- hn_throwaway_99 7y ago
  Use the right tool for the job. Array to potentially different sized array? Use flatMap (which he implements in his example, albeit not it an optimal way). Array to single object or value? Use reduce.

jrimbault 7y ago

That's also my minor nitpick, I feel like the syntax : `list.filter(myFilter).map(transform)` is clear about what I do and, each functions has a clear goal. Otherwise I enjoyed reading this.

mikeryan 7y ago
While your example reads a bit better, you’re now iterating through your list twice.
- fwip 7y ago
  Most code isn't performance-critical. This pattern will probably be dominated by the time taken to filter and map, not loop iteration.
- londt8 7y ago
  Technically there is no iteration in filter/map/reduce at all.
  - Stratoscope 7y ago
    That's incorrect. All of those functions are implemented using iteration. Consider this excerpt from the .map() polyfill on MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map#Polyfill https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe... // 7. Let k be 0 k = 0; // 8. Repeat, while k < len while (k < len) { // [loop body omitted] // d. Increase k by 1. k++; }
- saagarjha 7y ago
  Does JavaScript have adapters to covert lists into generators or lazy iterators?
  - hn_throwaway_99 7y ago
    Unfortunately not in a way that can optimize these methods. This is one reason the Java Streams API, which has a similar purpose (e.g. map, filter, flatMap, reduce, etc.), is a better design IMO because you can chain together method calls without creating (and iterating) the full array at each step.

_bxg1 7y ago

I think the intent was simply to teach. Obviously if something can be done with map() instead of reduce(), it'll be more readable as map(). But seeing how the other list functions can be made out of reduce() helps you understand how it works.

azangru 7y ago

> Almost all of these examples I'd argue would be better suited for something like .map() Roughly half of his examples take an array and return either a differently-sized array, or a different data structure altogether. I can’t imagine how one could argue for a map in these cases.

noir_lord 7y ago
Indeed, reduce is the swiss army knife since you can use it (sometimes when you shouldn't) to implement most of the other methods of map/filter etc.
hn_throwaway_99 7y ago
Use the right tool for the job. Array to potentially different sized array? Use flatMap (which he implements in his example, albeit not it an optimal way). Array to single object or value? Use reduce.