Switch statement for string matching in JavaScript

Question

How do I write a swtich for the following conditional   If the url contains  foo   then settings base url is  bar    The following is achieving the effect required but I ve a feeling this would be more manageable in a switch   var doc location   document location href  var url strip   new RegExp  http             var base url   url strip exec doc location  var base url string   base url 0      BASE URL CASES     LOCAL if  base url string indexOf  xxx local    gt  -1        settings              base url     http   xxx local                DEV if  base url string indexOf  xxx dev yyy com    gt  -1        settings              base url     http   xxx dev yyy com xxx

User · Accepted Answer

You can t do it in a switch unless you re doing full string matching  that s doing substring matching   This isn t quite true  as Sean points out in the comments  See note at the end    If you re happy that your regex at the top is stripping away everything that you don t want to compare in your match  you don t need a substring match  and could do   switch  base url string        case  xxx local              Blah         break      case  xxx dev yyy com              Blah         break         but again  that only works if that s the complete string you re matching  It would fail if base url string were  say   yyy xxx local  whereas your current code would match that in the  xxx local  branch     Update  Okay  so technically you can use a switch for substring matching  but I wouldn t recommend it in most situations  Here s how  live example    function test str        switch  true          case  xyz  test str           display      Matched  xyz  test            break        case  test  test str           display      Matched  test  test            break        case  ing  test str           display      Matched  ing  test            break        default          display      Didn t match any test            break            That works because of the way JavaScript switch statements work  in particular two key aspects  First  that the cases are considered in source text order  and second that the selector expressions  the bits after the keyword case  are expressions that are evaluated as that case is evaluated  not constants as in some other languages   So since our test expression is true  the first case expression that results in true will be the one that gets used

User · Answer

var token    spo    switch token       case    token match  spo      token   undefined            console log  MATCHED           break       default         console log  NO MATCH       break       --  If the match is made the ternary expression returns the original token ----  The original token is evaluated by case   --  If the match is not made the ternary returns undefined  ----  Case evaluates the token against undefined which hopefully your token is not   The ternary test can be anything for instance in your case         base url string indexOf  xxx dev yyy com      xxx dev yyy com   undefined                                                  token match  spo      token   undefined      is a ternary expression    The test in this case is token match  spo   which states the match the string held in token against the regex expression  spo    which is the literal string spo in this case     If the expression and the string match it results in true and returns token   which is the string the switch statement is operating on     Obviously token     token so the switch statement is matched and the case evaluated   It is easier to understand if you look at it in layers and understand that the turnery test is evaluated  BEFORE  the switch statement so that the switch statement only sees the results of the test

User · Answer

Just use the location host property  switch  location host        case  xxx local           settings               break      case  xxx dev yyy com           settings               break

User · Answer

Another option is to use input field of a regexp match result   str    XYZ test   switch  str      case  str match   xyz          input      console log  Matched a string that starts with  xyz         break    case  str match  test          input      console log  Matched the  test  substring                break    default      console log  Didn t match        break

User · Answer

You could also make use of the default case like this      switch  name            case  t               return filter getType            case  c               return  filter getCategory             default              if  name startsWith  f-                      return filter getFeatures  type  name

User · Answer

It may be easier  Try to think like this    first catch a string between regular characters after that find  case           www dev yyy com      xxx foo pl   var url    xxx foo pl    switch  url match            0       case   dev yyy               console log  xxx dev yyy com   break      case   some              console log  xxx foo pl   break      end switch

User · Answer

RegExp can be used on the input string not just technically but practically with the match method too   Because the output of the match   is an array we need to retrieve the first array element of the result  When the match fails  the function returns null  To avoid an exception error we will add the    conditional operator before accessing the first array element and test against the input property that is a static property of regular expressions that contains the input string   str    XYZ test   switch  str      case  str match   xyz          input      console log  Matched a string that starts with  xyz         break    case  str match  test          input      console log  Matched the  test  substring                break    default      console log  Didn t match        break      Another approach is to use the String   constructor to convert the resulting array that must have only 1 element  no capturing groups  and whole string must be captured with quanitifiers      to a string  In case of a failure the null object will become a  null  string  Not convenient   str    haystack   switch  str      case String str match   hay           console log  Matched a string that starts with  hay         break      Anyway  a more elegant solution is to use the   find-this-in  test str  with switch  true  method which simply returns a boolean value and it s easier to search without case sensitivity

User · Answer

Self-contained version that increases job security  switch  s match r    null   0     x000D   x000D  function identifyCountry hostname only gov false       const exceptionRe        uk ac eu        https   en wikipedia org wiki Country code top-level domain ASCII ccTLDs not in ISO 3166-1     const h   hostname split           const len   h length      const tld   h len-1       const sld   len  gt   2   h len-2    null       if  tld length    2             if  only gov  amp  amp  sld     gov    return null          switch     tld match exceptionRe      null    0                case  uk                 Britain owns uses this one             return  gb            case  ac                 Ascension Island is part of the British Overseas territory                Saint Helena  Ascension and Tristan da Cunha              return  sh            case null                2-letter TLD  not  in the exception list                it s a valid ccTLD corresponding to its country             return tld           default                2-letter TLD  in  the exception list  e g    eu                 it s not a valid ccTLD and we don t know the country             return null                  else if  tld     gov                AMERICAAA         return  us         else           return null          x000D   lt p gt Click the following domains  lt  p gt   lt ul onclick  console log    identifyCountry event target textContent    lt     event target textContent      gt       lt li gt example com lt  li gt       lt li gt example co uk lt  li gt       lt li gt example eu lt  li gt       lt li gt example ca lt  li gt       lt li gt example ac lt  li gt       lt li gt example gov lt  li gt   lt  ul gt  x000D   x000D   x000D   Honestly  though  you could just do something like function switchableMatch s r         returns the FIRST match of r on s  otherwise  null     const m   s match r       if m  return m 0       else return null     and then later switch switchableMatch s r

User · Answer

Might be too late and all  but I liked this in case assignment     function extractParameters args        function getCase arg  key            return arg match new RegExp    key                            args forEach  arg    gt            console log  arg      arg           let match          switch  arg                case  match   getCase arg   --user    input              case  match   getCase arg   -u    input                  userName   match 1                   break               case  match   getCase arg   --password    input              case  match   getCase arg   -p    input                  password   match 1                   break               case  match   getCase arg   --branch    input              case  match   getCase arg   -b    input                  branch   match 1                   break                         you could event take it further  and pass a list of option and handle the regex with

[javascript] Switch statement for string matching in JavaScript

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