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Re: some logic error on a map function

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JRough wrote:
> Jake Jarvis wrote:
>> JRough wrote

>>> I get the error :  unexpected end of input,  there is some logic
>>> error before it joins the words.
>>>

[ ... note: sentences here reduced from original ...]

>>> var sentences = [
>>>    "I now took ... with a chair.",
>>>    "But it was ... no yoking them.",
>>>    "I then placed ... settle down in.",
>>>    "But I ... the window, ... the night.",
>>>    "The devil ... violent knockings? ... dismissed it.",
>>>    "For who could tell ... knock me down!"
>>> ];
>>>
>>> var badwords = ['window', 'chair', 'knockings'];
>>>
>>>
>>> // Fill in function body here 
>>> var hasBadwords = function (message, index) {

[ ... implementation from OP removed ... ]

>>> };
>>> // Tell us what the output is from running this code:
>>> console.log(sentences.map(function (sentence, index) {
>>>    return hasBadwords(sentence) ? index : '';
>>> }).join(''));
>>>

>> The error message apparently is "Uncaught SyntaxError: Unexpected end
>> of input" and it is used by at least Chrome.
>> 
>> In Firefox the message is different: "SyntaxError: missing } after
>> function body".
>> 
>> Do you use an editor with syntax highlighting?
 
> I would still like this to work either way, Thomas' way or my way. 

Does this have anything to do with Jake's comment?  Please, you've been 
around here plenty long enough to know how to reduce quotes to the 
relevant minimum, to ask questions better than "it doesn't work -- 
help!", to note actual attempts to help and distinguish them from noisy 
attempts to prove a point.  Please contribute to the dialogue.



> It may be bogus but its an exercise of using the map function.  

The outer wrapper is certainly an appropriate use of `map`.  But for the 
function you've presumably been asked to write ("Fill in function body 
here") `map` makes little sense.  `map` is about applying a function to 
the value(s) of a container and returning a new container of the same 
shape.  In the case of `Array.prototype.map`, that container is always an 
array, but the concept is more general. [1]  However, all you want out of 
the function is a boolean that reports whether any of the bad words are 
included in the message.  `map` makes no sense.  After a little 
manipulation of the message string, you will have an array of words to 
test, but you do not want back an array of that same size as a result.

There are other functions more related to what you're doing here.  
Perhaps most fundamental is `reduce`, which fits the bill in one way, as 
the point of `reduce` is to take a container and fold it down into a 
single value, which sounds like what you want to do.  But `reduce` is 
bringing out the big guns.  It's overkill for this simple problem.

`filter` is somewhat more helpful, as it would allow you to find all the 
words which match a given predicate.  You *could* use this, and then 
check if the resulting length is positive.  But that is still overkill, 
because you are only asked to find the sentences that contain the 
forbidden words, not to document all the places in those sentences where 
the words occur.

There would also be ways to do this with `find`.  But I won't go into 
them, because there is clearly a right function for this: `some`.  All 
you want to know is whether there is some word in the list contained in 
the excluded set.  If you find one, you're done, and shouldn't need to 
test the rest.  While `find` would similarly stop when it finds a value, 
`find` returns the value; `some` returns a boolean to say that it has 
found something;  that latter is precisely what's desired here.  `some` 
is also supported by more implementations than `find`.

So here is one solution:

    var hasBadwords = function (message) {
      var words = message.replace(/[^\w\s]/g, '').split(/\s+/);
      return words.some(function(word) {
        return badwords.includes(word);
      });
    };

(Note that I dropped the unnecessary `index` parameter here.)

`includes` may not be supported where you need it, so you could use this 
work-around:

    var hasBadwords = function (message) {
      var words = message.replace(/[^\w\s]/g, '').split(/\s+/);
      return words.some(function(word) {
        return badwords.indexOf(word) > -1;
      });
    };

I would suggest that this is not wonderful code, as this function is not 
referentially transparent, depending on it does on the global `badwords` 
list.  I would prefer to see that as a parameter to this, or to see a 
function which accepted that and returned the equivalent of this function.

This is not to say that there is anything wrong with the regex solution 
proposed.  To my eyes this looks much closer to what's asked for in the 
problem.  However, if this is supposed to be an exercise in how to use 
`map`, then I think it's poorly designed.


  [1]: https://github.com/fantasyland/fantasy-land#functor

  -- Scott

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Thread

some logic error on a map function JRough <janis.rough@gmail.com> - 2016-06-15 20:23 -0700
  Re: some logic error on a map function Jake Jarvis <pig_in_shoes@yahoo.com> - 2016-06-16 09:58 +0200
    Re: some logic error on a map function "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2016-06-16 12:47 +0200
    Re: some logic error on a map function Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-06-16 12:55 +0200
      Re: some logic error on a map function Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-06-16 14:08 +0200
      Re: some logic error on a map function JRough <janis.rough@gmail.com> - 2016-06-16 11:04 -0700
      Re: some logic error on a map function JRough <janis.rough@gmail.com> - 2016-06-16 11:04 -0700
      Re: some logic error on a map function JRough <janis.rough@gmail.com> - 2016-06-17 13:30 -0700
      Re: some logic error on a map function JRough <janis.rough@gmail.com> - 2016-06-17 13:41 -0700
        Re: some logic error on a map function Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2016-06-17 23:10 +0200
    Re: some logic error on a map function JRough <janis.rough@gmail.com> - 2016-06-17 13:31 -0700
      Re: some logic error on a map function Scott Sauyet <scott@sauyet.com> - 2016-07-03 03:07 +0000
        Re: some logic error on a map function JRough <janis.rough@gmail.com> - 2016-07-09 11:38 -0700

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