Question 418801 in Javascript Question posted in
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Javascript – Error in implementation of 'switch' with regular expressions

The following snippet can be used as a bookmarklet to toggle between multiple websites or pages without typing or even remembering them. Here is the first version, it works fine:

let url;
switch (location.host) {
    case 'github.com':
        url = location.href;
        url = url.replace('github.com', 'stackoverflow.com');
        window.open(url, '_self');
        break;
    case 'stackoverflow.com':
    case 'superuser.com':
    case 'unix.stackexchange.com':
        url = location.href;
        url = url.replace('/.+/', 'www.reddit.com');
        window.open(url, '_self');
        break;
    case 'www.reddit.com':
        url = location.href;
        url = url.replace('www.reddit.com', 'github.com');
        window.open(url, '_self');
        break;
}

Then I tried to further improve it so that it will work not only for unix.stackexchange, but also for english.stackexchange.com, philosophy.stackexchange.com, bicycles.stackexchange.com, and so on.

For this, as suggested by T. J. Crowder in his 2010 answer: https://stackoverflow.com/a/2896642, I added regular expressions. But when I try it in the JavaScript console, it throws an error: SyntaxError: Unexpected token '.'. Expected a ')' or a ',' after a parameter declaration. Why is that, what exactly is wrong here?

function toggle(location.host) {
    let url;
    switch (true) {
        case 'github.com':
            url = location.href;
            url = url.replace('github.com', 'stackoverflow.com');
            window.open(url, '_self');
            break;
        case 'stackoverflow.com':
        case 'superuser.com':
        case /.+.stackexchange.com/.toggle(str):
            url = location.href;
            url = url.replace('/.+/', 'www.reddit.com');
            window.open(url, '_self');
            break;
        case 'www.reddit.com':
            url = location.href;
            url = url.replace('www.reddit.com', 'github.com');
            window.open(url, '_self');
            break;
    }
}
Tags:

2

Answers


  1. 0

    What may /.+.stackexchange.com/.toggle(str): mean? It must indeed throw something, because RegExp.toggle is a non existing method.

    When you use switch(true) you should make sure that every case is either true or false. Otherwise the result will be at least unpredictable. So in your case I suppose you should test a regular expression for each case:

    console.log(`location.host is ${location.host}`);
toggle(location.host);

function toggle(host) {
  let url;
  switch (true) {
    case /github.com/i.test(host):
      url = location.href;
      url = url.replace('github.com', 'stackoverflow.com');
      return console.log(url);
    case /stackoverflow.com/i.test(host):
    case /superuser.com/i.test(host):
    case /stackexchange.com/i.test(host):
      url = location.href;
      return console.log(`...${url} (unchanged)`);
    case /www.reddit.com/i.test(host):
      url = location.href;
      url = 'github.com';
      return console.log(url);
    case /stacksnippets.net/i.test(host):
      return console.log(`from stackoverflow snippet box`); 
    default:
      return console.log(`no matches`);
  }
}
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  2. 0

    The problem exposed in the question is a typo…

    The error is caused by this line:

    function toggle(location.host) {
// ---------------------^
// Can't use the dot here, in the parameter name.

    That’s because there is a parameter in the function with a dot (.) in the name when they can’t.

    The following line works just fine:

    function toogle(url=location.host) {
// -------------------------^
// Can use a dot here, in the parameter default value.

    Or, if you don’t want to let the URL change by the user, then just don’t receive parameters…

    function toogle() {
   const url = location.host

    Also, there’s this issue with the .toogle() that is not a RegExp method. If you’re trying to make some kind of loop to the toogle() function itself, then it’s a very dangerous idea and somewhat complicated to manage (because the function can enter in an infinite loop if not done correctly).

    There’s this other answer that, although it does not answer your question, gives a working solution to your needs…

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