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choonkeat/ElmUrlQuirk.md

Created December 3, 2022 04:04
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  1. choonkeat created this gist Dec 3, 2022.
    55 changes: 55 additions & 0 deletions ElmUrlQuirk.md
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    ```elm
    import Url
    import Url.Parser exposing ((<?>))
    import Url.Parser.Query

    "http://example.com/?key=Prefix%3A+Some+text+%2B+Some+words+%3D+Words+%40+%3CLast+word%3E"
    |> Url.fromString
    |> Maybe.andThen (Url.Parser.parse (Url.Parser.top <?> Url.Parser.Query.string "key"))
    --> Just (Just "Prefix: Some text + Some words = Words @ <Last word>")
    ```

    Test will fail

    ```
    Just (Just "Prefix: Some text + Some words = Words @ <Last word>")
    ╷
    │ Expect.equal
    ╵
    Just (Just "Prefix:+Some+text+++Some+words+=+Words+@+<Last+word>")
    ```

    Notice that

    ```js
    encodeURIComponent('Prefix: Some text + Some words = Words @ <Last word>')
    //=> 'Prefix%3A%20Some%20text%20%2B%20Some%20words%20%3D%20Words%20%40%20%3CLast%20word%3E'
    ```

    and indeed, using that as input URL, the test will pass

    ```diff
    import Url
    import Url.Parser exposing ((<?>))
    import Url.Parser.Query

    -"http://example.com/?key=Prefix%3A+Some+text+%2B+Some+words+%3D+Words+%40+%3CLast+word%3E"
    +"http://example.com/?key=Prefix%3A%20Some%20text%20%2B%20Some%20words%20%3D%20Words%20%40%20%3CLast%20word%3E"
    |> Url.fromString
    |> Maybe.andThen (Url.Parser.parse (Url.Parser.top <?> Url.Parser.Query.string "key"))
    --> Just (Just "Prefix: Some text + Some words = Words @ <Last word>")
    ```

    So, the workaround is actually to augment `Url.fromString`

    ```diff
    import Url
    import Url.Parser exposing ((<?>))
    import Url.Parser.Query

    "http://example.com/?key=Prefix%3A+Some+text+%2B+Some+words+%3D+Words+%40+%3CLast+word%3E"
    +|> String.replace "+" "%20"
    |> Url.fromString
    |> Maybe.andThen (Url.Parser.parse (Url.Parser.top <?> Url.Parser.Query.string "key"))
    --> Just (Just "Prefix: Some text + Some words = Words @ <Last word>")
    ```