6 ms·

Higher-Order Functions in JavaScript

136 points by zatkin 12y ago

VieElm 12y ago
In ES6 there are iterables that one uses `for...of` with. Rauschmayer of 2ality has said that `for...of` should be used instead of forEach and I wonder how that will affect composability in functional programming. I quite like the concept of iteratables and creating data structures that can make use of for of and generators. I just have thought about how that affects functional style programming.
- bzbarsky 12y ago
  for..of simply desugars into getting an iterator from the iterable and then iterating it, right? To compose iterables, you'd presumably work with iterators directly instead of the sugar.
zatkin 12y ago
It's also worth mentioning Lodash[1] if you're new to this idea of functional programming. They have an awesome description of each function name and they're very closely aligned to the functional terminology. [1] - http://lodash.com/docs http://lodash.com/docs
- pmlamotte 12y ago
  Lodash is what finally made me get functional programming, because I was able to start using it in small places where it made sense as opposed to diving into it all at once. At first it started out with just map and filter for some basic cases. Then I would peruse the Lodash docs now and then and discover functions that could replace a lot of my iterative, often messy code with something that felt much more elegant, especially with chaining. With that new-found knowledge, I decided to make my 4th or 5th attempt at trying to grasp clojure and ran through some 4clojure problems. This time I breezed through the problems, and in many cases enjoyed writing it more than I would have in a typical iterative style. I made sure to follow some recommended users to see their solutions as well, which helped reduce much of my parentheses bloat. My favorite thing about using high order functions has been that provided your underlying functions are tested/correct, you can more easily reason about and test your new functions, particularly when you keep things immutable/side-effect free. I'm sure I would have gotten to this point eventually without Lodash, but being able to make use of bits and pieces at a time was a major catalyst for me.
- dominotw 12y ago
  Also this ? http://ramdajs.com/ http://ramdajs.com/
  - masklinn 12y ago
    Also this: http://facebook.github.io/immutable-js/docs/#/ http://facebook.github.io/immutable-js/docs/#/ and this: http://swannodette.github.io/mori/ http://swannodette.github.io/mori/
    - zatkin 12y ago
      Wow, this is wonderful input. I always love finding an overlap in terminology. If you find the same description of something in more than two places, I think it's safe to say that it's some kind of standard definition.
- k__ 12y ago
  But for a functional library it has strange argument ordering.
  - flannelhead 12y ago
    There's a variant of lodash with auto-currying and better argument ordering: https://github.com/lodash/lodash-fp https://github.com/lodash/lodash-fp I haven't tried it, but it looks like it could basically replace Ramda (although I feel that Ramda might contain even more FP oriented functions).
    - k__ 12y ago
      I see. Nice :) My library of choice is http://www.preludels.com http://www.preludels.com
      - klibertp 12y ago
        prelude-ls really shines when combined with LiveScript - syntactic support for partial application, currying, function composition, "pipelining" (|>), implicit arguments and so much more really make a difference. I started writing a comparison between un-sugared JS and LS use for functional programming patterns, here: https://klibert.pl/warsawjs-talk/code.html https://klibert.pl/warsawjs-talk/code.html (for the talk I gave: https://klibert.pl/warsawjs-talk/ https://klibert.pl/warsawjs-talk/). That being said, I'm very interested in mori, immutable-js or lz.js. prelude-ls is nice, but is designed to work with native JS types and provides no extended semantics that I'd find useful. It's still my go-to library when working on the frontend and it probably will remain one, but I'm thinking about contributing some support for other advanced collection types to it.
    - tobr 12y ago
      After a little bit of use, I feel like lodash-fp is limited by being a simple adaptation of lodash. Lodash's API is designed around variadic functions, which doesn't really work with autocurrying, so a bunch of important options and functionality is lost. On the other hand, working with Ramda makes me miss some of the flexibility of lodash - e.g., not having to use a different map() for arrays and objects. The optimal functional utility library would be designed with autocurrying in mind from the start, but not shy away from flexibility where it makes sense.
- thomasvarney723 12y ago
  Here's a good video showing the difference between underscore and lodash: https://www.youtube.com/watch?v=m3svKOdZijA https://www.youtube.com/watch?v=m3svKOdZijA
amelius 12y ago
> The second relies on two external functions and is one line long. > console.log(sum(range(1, 10))); > Which one is more likely to contain a bug? I'd say the second one. Because the first one is totally transparent. The second one relies on functions I can't see. Especially the "range" function may cause problems because here it generates the full range, including both delimiters, unlike the range function in e.g. python. EDIT: functional programming is extremely useful, but I don't think this example really highlights the most important advantages.
- netcraft 12y ago
  but sum and range are able to be tested in isolation and will be reused across the application, making a bug in them more visible - rather than repeating the logic of the loop in every instance where you need a loop. Also, when maintaining the code later, the signal to noise ratio is much higher, you can see exactly what is being attempted, not the implementation details of it. There are certainly times when you need to see the implementation details or that your needs don't fit the prescribed and available functions (eg, range being exclusive vs inclusive), but then if that is the exception rather than the rule, it will serve as another indicator when you come across that code that `this is doing something different than usual`, so pay attention to the details.
  - deleted 12y ago
    [deleted]
  - iopq 12y ago
    and then you forget range(1, 10) is a half-open interval because it's meant to be used with `length` as in `range(0, foo.length)`
    - serrimo 12y ago
      That part has always annoyed me. But then Python beat me into submission with its seductive collection comprehension... Now I see it as a standard convention, like indexing should start with 0.
- deleted 12y ago
drderidder 12y ago
I recently read this, worked through the examples, and was pleasantly surprised at the depth and quality. Subsequently we recommended it to our 800+ member meetup group as the top learning resource for new JS programmers. The content is enlightening and enjoyable and could be just the thing for reaching a breakthrough in understanding about functional programming.
- heatish 12y ago
  Eloquent Javascript was the first programming book that I ever worked through online and subsequently went and bought because I was so happy with it. I was young and playing Diablo 2: LoD and stumbled upon some bot that would let me do Mephisto runs for loot all night, I was amazed with it and went back to the forums where I'd found it and did some reading, this was the book that they recommended for anyone who was interested in learning some programming. I'd have to say that this book was one of the more gentle and concise introductory books I've ever read and so far I couldn't be happier that it was my personal introduction to JS and programming. It certainly set me leaps ahead in the JS section when I attended a web dev bootcamp. It is my personal go to for any of my friends who approach me about their interest in getting started with programming. Big Nerd Ranch books are a close second but I've only recently found them and begun reading them.
  - mauz 12y ago
    I profoundly appreciate the nostalgia you brought back by talking about Mephisto runs.
killtheliterate 12y ago
I love this book for it's, ah, eloquent and inclusive way of describing more advanced JS topics. Definitely of value, even for the more experienced JS dev.
arcticf0x 12y ago
great book!
osconfused 12y ago
On the topic of functional JavaScript, a few interesting articles and books I have been reading that have helped shed more light on this subject matter. I particularly enjoyed the Functional JavaScript book [2]. [1] - http://www.cse.chalmers.se/~rjmh/Papers/whyfp.pdf http://www.cse.chalmers.se/~rjmh/Papers/whyfp.pdf [2] - http://shop.oreilly.com/product/0636920028857.do http://shop.oreilly.com/product/0636920028857.do [3] - http://stackoverflow.com/questions/36504/why-functional-languages http://stackoverflow.com/questions/36504/why-functional-lang... [4] - http://scott.sauyet.com/Javascript/Talk/2014/01/FuncProgTalk/#slide-0 http://scott.sauyet.com/Javascript/Talk/2014/01/FuncProgTalk...
deleted 12y ago
[deleted]
romaniv 12y ago
The theory is good, but the specifics of JS syntax, the type system, and the lack of support from the standard library make functional programming much less fun to use than in proper functional languages or even C#.
leeoniya 12y ago
in case anyone missed it, it's by the author of CodeMirror [1], Acorn, Tern, etc. [2]. He also contributes to Rust. [1] https://github.com/codemirror/codemirror https://github.com/codemirror/codemirror [2] https://github.com/marijnh https://github.com/marijnh

136 points by zatkin 12y ago

In ES6 there are iterables that one uses `for...of` with. Rauschmayer of 2ality has said that `for...of` should be used instead of forEach and I wonder how that will affect composability in functional programming. I quite like the concept of iteratables and creating data structures that can make use of for of and generators. I just have thought about how that affects functional style programming.

bzbarsky 12y ago
for..of simply desugars into getting an iterator from the iterable and then iterating it, right? To compose iterables, you'd presumably work with iterators directly instead of the sugar.

zatkin 12y ago

It's also worth mentioning Lodash[1] if you're new to this idea of functional programming. They have an awesome description of each function name and they're very closely aligned to the functional terminology. [1] - http://lodash.com/docs http://lodash.com/docs

pmlamotte 12y ago
Lodash is what finally made me get functional programming, because I was able to start using it in small places where it made sense as opposed to diving into it all at once. At first it started out with just map and filter for some basic cases. Then I would peruse the Lodash docs now and then and discover functions that could replace a lot of my iterative, often messy code with something that felt much more elegant, especially with chaining. With that new-found knowledge, I decided to make my 4th or 5th attempt at trying to grasp clojure and ran through some 4clojure problems. This time I breezed through the problems, and in many cases enjoyed writing it more than I would have in a typical iterative style. I made sure to follow some recommended users to see their solutions as well, which helped reduce much of my parentheses bloat. My favorite thing about using high order functions has been that provided your underlying functions are tested/correct, you can more easily reason about and test your new functions, particularly when you keep things immutable/side-effect free. I'm sure I would have gotten to this point eventually without Lodash, but being able to make use of bits and pieces at a time was a major catalyst for me.
dominotw 12y ago
Also this ? http://ramdajs.com/ http://ramdajs.com/
- masklinn 12y ago
  Also this: http://facebook.github.io/immutable-js/docs/#/ http://facebook.github.io/immutable-js/docs/#/ and this: http://swannodette.github.io/mori/ http://swannodette.github.io/mori/
  - zatkin 12y ago
    Wow, this is wonderful input. I always love finding an overlap in terminology. If you find the same description of something in more than two places, I think it's safe to say that it's some kind of standard definition.
k__ 12y ago
But for a functional library it has strange argument ordering.
- flannelhead 12y ago
  There's a variant of lodash with auto-currying and better argument ordering: https://github.com/lodash/lodash-fp https://github.com/lodash/lodash-fp I haven't tried it, but it looks like it could basically replace Ramda (although I feel that Ramda might contain even more FP oriented functions).
  - k__ 12y ago
    I see. Nice :) My library of choice is http://www.preludels.com http://www.preludels.com
    - klibertp 12y ago
      prelude-ls really shines when combined with LiveScript - syntactic support for partial application, currying, function composition, "pipelining" (|>), implicit arguments and so much more really make a difference. I started writing a comparison between un-sugared JS and LS use for functional programming patterns, here: https://klibert.pl/warsawjs-talk/code.html https://klibert.pl/warsawjs-talk/code.html (for the talk I gave: https://klibert.pl/warsawjs-talk/ https://klibert.pl/warsawjs-talk/). That being said, I'm very interested in mori, immutable-js or lz.js. prelude-ls is nice, but is designed to work with native JS types and provides no extended semantics that I'd find useful. It's still my go-to library when working on the frontend and it probably will remain one, but I'm thinking about contributing some support for other advanced collection types to it.
  - tobr 12y ago
    After a little bit of use, I feel like lodash-fp is limited by being a simple adaptation of lodash. Lodash's API is designed around variadic functions, which doesn't really work with autocurrying, so a bunch of important options and functionality is lost. On the other hand, working with Ramda makes me miss some of the flexibility of lodash - e.g., not having to use a different map() for arrays and objects. The optimal functional utility library would be designed with autocurrying in mind from the start, but not shy away from flexibility where it makes sense.
thomasvarney723 12y ago
Here's a good video showing the difference between underscore and lodash: https://www.youtube.com/watch?v=m3svKOdZijA https://www.youtube.com/watch?v=m3svKOdZijA

amelius 12y ago

> The second relies on two external functions and is one line long. > console.log(sum(range(1, 10))); > Which one is more likely to contain a bug? I'd say the second one. Because the first one is totally transparent. The second one relies on functions I can't see. Especially the "range" function may cause problems because here it generates the full range, including both delimiters, unlike the range function in e.g. python. EDIT: functional programming is extremely useful, but I don't think this example really highlights the most important advantages.

netcraft 12y ago
but sum and range are able to be tested in isolation and will be reused across the application, making a bug in them more visible - rather than repeating the logic of the loop in every instance where you need a loop. Also, when maintaining the code later, the signal to noise ratio is much higher, you can see exactly what is being attempted, not the implementation details of it. There are certainly times when you need to see the implementation details or that your needs don't fit the prescribed and available functions (eg, range being exclusive vs inclusive), but then if that is the exception rather than the rule, it will serve as another indicator when you come across that code that `this is doing something different than usual`, so pay attention to the details.
- deleted 12y ago
  [deleted]
- iopq 12y ago
  and then you forget range(1, 10) is a half-open interval because it's meant to be used with `length` as in `range(0, foo.length)`
  - serrimo 12y ago
    That part has always annoyed me. But then Python beat me into submission with its seductive collection comprehension... Now I see it as a standard convention, like indexing should start with 0.
deleted 12y ago

drderidder 12y ago

I recently read this, worked through the examples, and was pleasantly surprised at the depth and quality. Subsequently we recommended it to our 800+ member meetup group as the top learning resource for new JS programmers. The content is enlightening and enjoyable and could be just the thing for reaching a breakthrough in understanding about functional programming.

heatish 12y ago
Eloquent Javascript was the first programming book that I ever worked through online and subsequently went and bought because I was so happy with it. I was young and playing Diablo 2: LoD and stumbled upon some bot that would let me do Mephisto runs for loot all night, I was amazed with it and went back to the forums where I'd found it and did some reading, this was the book that they recommended for anyone who was interested in learning some programming. I'd have to say that this book was one of the more gentle and concise introductory books I've ever read and so far I couldn't be happier that it was my personal introduction to JS and programming. It certainly set me leaps ahead in the JS section when I attended a web dev bootcamp. It is my personal go to for any of my friends who approach me about their interest in getting started with programming. Big Nerd Ranch books are a close second but I've only recently found them and begun reading them.
- mauz 12y ago
  I profoundly appreciate the nostalgia you brought back by talking about Mephisto runs.

killtheliterate 12y ago

I love this book for it's, ah, eloquent and inclusive way of describing more advanced JS topics. Definitely of value, even for the more experienced JS dev.

arcticf0x 12y ago

great book!

osconfused 12y ago

On the topic of functional JavaScript, a few interesting articles and books I have been reading that have helped shed more light on this subject matter. I particularly enjoyed the Functional JavaScript book [2]. [1] - http://www.cse.chalmers.se/~rjmh/Papers/whyfp.pdf http://www.cse.chalmers.se/~rjmh/Papers/whyfp.pdf [2] - http://shop.oreilly.com/product/0636920028857.do http://shop.oreilly.com/product/0636920028857.do [3] - http://stackoverflow.com/questions/36504/why-functional-languages http://stackoverflow.com/questions/36504/why-functional-lang... [4] - http://scott.sauyet.com/Javascript/Talk/2014/01/FuncProgTalk/#slide-0 http://scott.sauyet.com/Javascript/Talk/2014/01/FuncProgTalk...

deleted 12y ago

[deleted]

romaniv 12y ago

The theory is good, but the specifics of JS syntax, the type system, and the lack of support from the standard library make functional programming much less fun to use than in proper functional languages or even C#.

leeoniya 12y ago

in case anyone missed it, it's by the author of CodeMirror [1], Acorn, Tern, etc. [2]. He also contributes to Rust. [1] https://github.com/codemirror/codemirror https://github.com/codemirror/codemirror [2] https://github.com/marijnh https://github.com/marijnh