Switch Case Regex Test

Question

var path = location.pathname;
 switch(path){
  case (/\/memberlist/).test(path) :getCSS('url-22.css'); break;
  case (/\/register/).test(path):  getCSS('url-6.css');  break;
  case (/buy-credits/g).test(path): getCSS('url-7.css'); break;
  case (/\/?u(\d+)friends$/).test(path): getCSS('url-8.css'); break;
  case (/\/privmsg/).test(path): getCSS('url-9.css'); break;
  case (/\/?u(\d+)wall$/).test(path): getCSS('url-4.css'); break;
 }
  function getCSS(url,media){
       var a = document.createElement('link');
           a.href=url;
           a.media= media || 'screen';
           a.rel="stylesheet";
     return (document.getElementsByTagName('head')[0].appendChild(a));    
  }

That is my code, and for some reason it's not running the function that should run. For testing purpose we could change var path="/memberlist" and it still won't run. Can someone explain to me why this won't run. Don't really use switch statements

switch you always compare with path. So make your string you enter tehre the same as path. for use of substring like you try see here :http://stackoverflow.com/questions/2896626/switch-statement-for-string-matching-in-javascript — chillworld, Feb 11 '14 at 06:37

score 10 · Answer 1 · answered Feb 11 '14 at 06:45

10

change

switch(path){

to

switch(true){

as you can see in thread I'm reffering to in comment.

answered Feb 11 '14 at 06:45

chillworld

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Yes I saw this earlier, though after anubhava explained it I understood why it wasn't returning anything and that's because what it was looking for wasn't true or false. it works now thanks. – EasyBB Feb 11 '14 at 06:47
Related answer that has an example: https://stackoverflow.com/a/47281232/2193968 – Jerry Jeremiah Nov 19 '19 at 21:14

score 8 · Answer 2 · answered Apr 13 '17 at 17:08

8

None of the answers posted show a correct method to use a RegExp pattern in a switch case so I thought I'd post:

switch (myVar) {
   case 'case1':
      /...do work
      break
   case /[a-z]*/.test(myVar) && myVar:
      /...regex match, do work
      break
}

answered Apr 13 '17 at 17:08

Cory Robinson

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This works nicely. May I ask what is the AND for though and why does it not work without it? – JustAGuy Oct 11 '17 at 13:07
@gilfalko the && myVar is required because the switch is looking for a case where the parameter matches so we do the && to make the match only when the regex is true. – Cory Robinson Oct 11 '17 at 13:12
You can remove the && and change the parameter to 'true' as in @chillworld's example and it will work as well – Cory Robinson Oct 11 '17 at 13:14
But doesnt regex.test() by itself return a true\false if we have a match? – JustAGuy Oct 11 '17 at 14:42
This seems to be the correct answer based on the question asked. Exactly what I was looking for. – MuffinTheMan Apr 11 '19 at 03:31

score 2 · Accepted Answer · answered Feb 11 '14 at 06:37

2

switch-case doesn't work that way.

regex.test() method returns a boolean (true/false) and you are comparing that against the input string itself which will not be true for any of the case statement.

You need to convert switch-case into multiple if / else if / else block to execute your logic.

answered Feb 11 '14 at 06:37

anubhava

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Oh so the switch would have to be set for true? – EasyBB Feb 11 '14 at 06:38
For your updated answer, I just changed the switch to true and it's working now perfectly fine. I changed it from an `if / else if / else` so it was minimized and not so cluttered. – EasyBB Feb 11 '14 at 06:39
switch is useful only when multiple values need to be matched, here you will get either true or false from `regex.test()` method. – anubhava Feb 11 '14 at 06:40
That is true, which if none exist it'll break. – EasyBB Feb 11 '14 at 06:42
@anubhava actually it can see the link I set in comment. He's trying to do substring switching. but he need to switch for true and not path – chillworld Feb 11 '14 at 06:43
There will be multiple times I would have to write an `else if` and I don't want to do that, and in size and readability switch statement is the best option, no? Maybe I'm not getting your point. – EasyBB Feb 11 '14 at 06:44
You can avoid all switch and if completely. If I have to do it I would store all my regex in an array and call `test()` while iterating the array and breaking out as soon we get a match. Link provided by @chillworld also have a work-around to use `switch(true)` for this type of use-case. – anubhava Feb 11 '14 at 06:47
Yes looping is plausible for the situation, though I'm working on this code for a friend and don't feel like telling him how to update it, well explaining it to him. Thanks guys. – EasyBB Feb 11 '14 at 06:49

KooiInc · Answer 4 · 2014-02-11T07:25:23.487

Just for the record, the switch case could be rewritten to:

getCSS(
    /\/memberlist/).test(path)    && 'url-22.css' ||
    /\/register/).test(path)      && 'url-6.css'  ||
    /buy-credits/g).test(path)    && 'url-7.css'  ||
    /\/?u(\d+)friends$/)          && 'url-8.css'  ||
    /\/privmsg/).test(path)       && 'url-9.css'  ||
    /\/?u(\d+)wall$/).test(path)  && 'url-4.css'  || 
    'default'
);

Or rewrite getCSS, using a helper object

var path2url = {
   css: [
                {re: /\/register/, css: 'url-22.css'},
                {re: /buy-credits/g, css: 'url-6.css'},
                {re: /\/?u(\d+)friends$/, css: 'url-8.css'},
                {re: /\/privmsg/, css: 'url-8.css'},
                {re: /\/?u(\d+)wall$/, css: 'url-4.css'}
        ],
   getURL: function(path) {
     var i = this.css.length;
     while (--i) {
       if (this.css[i].re.test(path)) {
         return this.css[i].css;
       }
     }
     return null; // or something default
   }
};

function getCSS(path,media){
  var a = document.createElement('link');
  a.href= path2url.getURL(path); // <=
  a.media= media || 'screen';
  a.rel="stylesheet";
  return (document.getElementsByTagName('head')[0].appendChild(a));    
}

score 0 · Answer 5 · answered Jun 21 '17 at 07:00

0

Have a look

switch(str){
    case (/(abc|xyz)/.test(str) ? str : false):
        // Do some stuff
        break;
    default:
        // Do default stuff         
}

answered Jun 21 '17 at 07:00

DebuggerCoder

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Why -1 for this answer ? – DebuggerCoder Jun 29 '17 at 06:11
Did you even tried your own code? Your case returns true or false but you're matching the boolean with a string. You have to change `switch(str)` to `switch(true)` to get this to work. Also the additional bool-check isn't neccessary, since `test()` already returns true or false. – Pandora Dec 02 '18 at 19:37

Switch Case Regex Test

5 Answers5