On Saturday, July 4, 2020 at 11:40:32 PM UTC-7, Jake wrote:
>
> I wrote this and it actually works:
> \define video(url, w:"400px", h:"300px")
> <iframe width="$w$" height="$h$" src="""$url$""" frameborder="0"
> allowfullscreen></iframe>
> \end
> but I don't want to manually change
> https://www.youtube.com/watch?v=VIDEOID to
> https://www.youtube.com/embed/VIDEOID. I think I already know what
> should be done: "removeprefix" of "https://www.youtube.com/watch?v="; and
> "addprefix" of "https://www.youtube.com/embed/"; if the whole url is
> inserted or just addprefix if that's only VIDEOID, "but"... I don't know
> what the proper syntax should be ¯\_(ツ)_/¯ . (as well as I don't quite
> understand that "triple quotes" thingy).
>
First, the "triple quotes" thingy:
When substituting the $url$ macro parameter value into the iframe, there is
a possibility, no matter how remote, that the $url$ value could contain
double-quote characters ("). In that case, if the iframe parameter was
just src="...", then the substitution would result in nested or unmatched
quotes (i.e., src="http://stuff?arg="quoted stuff"&more=123&..."), which
would break the syntax since nested quotes are not handled by HTML
parameters. To address this, TiddlyWiki extends the normal HTML parameter
syntax to enable use of tripled double-quotes as outer delimiters so that
the enclosed text can contain instances of double-quotes without breaking.
Note that the same nested quotes issue can also be resolved by using
single-quotes (i.e., src='...' - supported by standard HTML) or even
doubled squarebrackets (i.e., src=[[...]] - another TiddlyWiki syntax
extension).
Next, how to do the removeprefix/addprefix filter:
In addition to the special quote handling described above, TiddlyWiki
extends the normal HTML parameter syntax to allow use of "inline filters"
(the tripled curly braces stuff).
To achieve your desired results, you would write the iframe's src="..."
parameter like this:
src={{{
[[$url$]removeprefix[https://www.youtube.com/watch?v=]addprefix[https://www.youtube.com/embed/]]
}}}
The first part of the filter simply starts with the provided url as literal
text (i.e, enclosed in square brackets). Then, the removeprefix[...]
filter operator is applied to that text, followed by the addprefix[...]
filter operator. The end result is the desired URL text, which is then
used as the value of the HTML src=... parameter. Note that the entire
filter syntax is contained in a matched set of outer square brackets, which
is then contained in the tripled curly braces that indicate use of an
inline filter.
Using the inline filter, your macro definition would look like this:
\define video(url, w:"400px", h:"300px")
<iframe width="$w$" height="$h$" src={{{
[[$url$]removeprefix[https://www.youtube.com/watch?v=]addprefix[https://www.youtube.com/embed/]]
}}} frameborder="0" allowfullscreen></iframe>
\end
One more note... to make the code a bit easier to understand, you could use
a couple of variables to define the values of the prefixes and the modified
src URL, like this:
\define video(url, w:"400px", h:"300px")
<$vars old="https://www.youtube.com/watch?v="; new=
"https://www.youtube.com/embed/";>
<$vars src={{{ [[$url$]removeprefix<old>addprefix<new>] }}}>
<iframe width="$w$" height="$h$" src=<<src>> frameborder="0" allowfullscreen
></iframe>
</$vars>
</$vars>
\end
As you can see, TiddlyWiki filter syntax can be a bit confusing at first
but it's also VERY powerful and can help you achieve lots of magical stuff.
enjoy,
-e
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