This macro:
- accepts a WTForm form field as a parameter
- renders a form field which follows the GOV.UK Elements patterns, both visually
and in markup terms
It then changes any page which uses either:
- the old, non-WTForms macro or
- the old, WTFforms `render_field` macro
…to use this new macro and removes both of the old ones.
It also adds the option to display hint text above the textbox.
For pages where
- we want you to be sure that you want to do what you’re about to do
- we want to be sure it’s you trying to do the thing
This adds a page that asks the user to confirm their password.
Users can add placeholders to their messages, eg
> …your vehicle ((registration number))
when the message is sent, this gets replaced with the data the user uploads, eg
> …your vehicle LC12 BFL
We reckon that it will be useful to see that the placeholder has been
recognised, ie that its syntax is correct, before uploading any data.
We reckon that the best way to do this is by styling it differently to the rest
of the text that the user types.
This is not a trivial problem. There are two possible ways to do it:
1 Write a Google Docs-style text rendering engine, which completely replaces
the native HTML `<textarea>` with a custom control, and programme what should
happen when the user types something that looks like a placeholder, or
presses an arrow key, or makes a selection, or…
2 Leave the `<textarea>` in place, unmodified, and duplicate layers in front
of/behind it to visually replace a placeholder with the blue lozenge
Unsurprisingly, this commit implements 2.
There are four layers. Each layer contains live-updated copy of the text in the
textbox, and each is styled differently:
- one layer behind the textbox to make the blue background
- the textbox itself
- a layer with the white text, which overlays the black text of the textbox
- a layer with an inner shadow to knock back the brackets
This is because of some interesting limitations:
- The text in the foreground and background must occupy the same physical space,
so no deleting characters from the duplicated layers
- Words can’t be split up into multiple elements,
eg `<span>((</span>regist…`:—this results in slightly different kerning to
`((regis…`, which messes up the alignment of the layers
- The textbox can’t be completely overlapped with a block of colour, because
the cursor disappears behind it. Trying to edit text when you can’t see the
cursor is hard.
Implementation
Technically this makes use of Paul Hayes work on Javascript modules in the
GOV.UK frontend toolkit[1].
It also makes use of the `oninput` event to detect changes to the textbox’s
contents. This is much more performant than `onkeydown`, `onpaste`, etc. Without
it the delay between user input and the layers all updating is too slow and you
see misalignment of the layers.
1. https://github.com/alphagov/govuk_frontend_toolkit/pull/227
