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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: How to perform an EXACT match for an item without looping through?
Date: Fri, 05 May 2017 18:40:08 +0200
Organization: PointedEars Software (PES)
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JJ wrote:

> On Wed, 3 May 2017 05:58:25 -0700 (PDT), justaguy wrote:
>> Sorry, it must be a misunderstanding.  For instance,
>> list.indexOf('12345') produces "found", which is wrong because it's not
>> the same as '123456', the latter is an item from the list while the
>> '12345' is not.
> 
> In that case...
> 
>   var list = "2332,123456,9922";
> 
>   var f = list.split(",").indexOf("12345");
>   console.log(f); //-1
>   var f = list.split(",").indexOf("123456");
>   console.log(f); //1

That would have been my suggestion, too.  (With the exception of the 
identifier, see below.)

> As for regexp...
> 
>   var f = list.match(/\b12345'b/g);
                               ^
  var f = list.match(/\b12345\b/g);

>   if (f.length == 0) {

String.prototype.match() returns “null” if there is no match, therefore
this code will throw the exception “null has no properties” in that case.  
The proper test is

  if (f === null)

Or simpler:

  if (f == null)

Or even simpler:

  if (!f)

>     console.log('not found');
>   }
>   else {
>     console.log('found');
>   }

And since double negation should be avoided in favor of clarity,

  if (f)
  {
    console.log("found");
  }
  else
  {
    console.log("not found");
  }

“f” is not a wise identifier for potential matches.

If the matches are not used, String.prototype.match() is the wrong method to 
call, and the “g”(lobal) flag is superfluous.  Instead, call 
RegExp.prototype.test():

  if (/\b12345\b/.test(list))
  {
    console.log("found");
  }
  else
  {
    console.log("not found");
  }

Note that if "the needle" is not fixed, RegExp-special characters might need 
to be escaped before passing them to the RegExp(-like) constructor.

-- 
PointedEars
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