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') > -1) {
    settings = {
        "base_url" : "http://xxx.local/"
    };
}

// DEV
if (base_url_string.indexOf('xxx.dev.yyy.com') > -1) {
    settings = {
        "base_url" : "http://xxx.dev.yyy.com/xxx/"
    };
}

Answer 1

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.