196. TD Using the Form State

Jul 21, 2026 02:05 · 4:27 · English · Whisper Turbo · 1 Speaker
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S… Speaker 1 (196. TD Using the Form State)
In the last lecture we found out that Angular tracks the state of
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S… Speaker 1 (196. TD Using the Form State)
each control of the form,
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whether it's valid and so on,
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and conditionally also adds these CSS classes.
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S… Speaker 1 (196. TD Using the Form State)
Now with that information we can go back to our form
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and you take advantage of it.
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S… Speaker 1 (196. TD Using the Form State)
Before diving into these CSS classes,
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S… Speaker 1 (196. TD Using the Form State)
the easiest way of taking advantage is down here on the submit button.
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S… Speaker 1 (196. TD Using the Form State)
Let's disable the button if the form is not valid.
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S… Speaker 1 (196. TD Using the Form State)
So I'll just split this over multiple lines and add some property
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S… Speaker 1 (196. TD Using the Form State)
binding.
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S… Speaker 1 (196. TD Using the Form State)
I want to bind to the disabled property,
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S… Speaker 1 (196. TD Using the Form State)
which will add the,
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S… Speaker 1 (196. TD Using the Form State)
or which will set the disabled state of this button to true or false
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S… Speaker 1 (196. TD Using the Form State)
depending on some condition,
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S… Speaker 1 (196. TD Using the Form State)
and I will specify the condition here.
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S… Speaker 1 (196. TD Using the Form State)
Now, I could say true here to always disable it.
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S… Speaker 1 (196. TD Using the Form State)
That, of course,
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S… Speaker 1 (196. TD Using the Form State)
is not super useful.
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S… Speaker 1 (196. TD Using the Form State)
Instead,
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S… Speaker 1 (196. TD Using the Form State)
here I want to check whether the form,
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S… Speaker 1 (196. TD Using the Form State)
remember,
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S… Speaker 1 (196. TD Using the Form State)
we do have access to it on this F local reference here.
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S… Speaker 1 (196. TD Using the Form State)
So if this form is valid,
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S… Speaker 1 (196. TD Using the Form State)
or to be precise,
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S… Speaker 1 (196. TD Using the Form State)
if it is not valid.
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S… Speaker 1 (196. TD Using the Form State)
So if this form is not valid,
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S… Speaker 1 (196. TD Using the Form State)
the button should be disabled.
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S… Speaker 1 (196. TD Using the Form State)
And we can actually see this once this reloads,
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S… Speaker 1 (196. TD Using the Form State)
that now the button is disabled.
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S… Speaker 1 (196. TD Using the Form State)
And only if I enter some valid values here,
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S… Speaker 1 (196. TD Using the Form State)
I can hit the submit button again.
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S… Speaker 1 (196. TD Using the Form State)
So this is the first improvement in place.
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S… Speaker 1 (196. TD Using the Form State)
The second improvement is to take advantage of these CSS
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classes.
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S… Speaker 1 (196. TD Using the Form State)
We do get these classes added automatically.
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S… Speaker 1 (196. TD Using the Form State)
So we can now go to the style sheet of this app component.
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S… Speaker 1 (196. TD Using the Form State)
And we could say that on ng -invalid,
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S… Speaker 1 (196. TD Using the Form State)
we want to give it a red border.
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S… Speaker 1 (196. TD Using the Form State)
So one pixel solid red.
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S… Speaker 1 (196. TD Using the Form State)
Sounds like a solid idea,
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S… Speaker 1 (196. TD Using the Form State)
doesn't it?
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S… Speaker 1 (196. TD Using the Form State)
Well, if we do this,
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S… Speaker 1 (196. TD Using the Form State)
you see everything is red now.
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S… Speaker 1 (196. TD Using the Form State)
The two controls,
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S… Speaker 1 (196. TD Using the Form State)
but also the overall form.
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S… Speaker 1 (196. TD Using the Form State)
The reason for this is that our overall form is also
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S… Speaker 1 (196. TD Using the Form State)
invalid and that Angular also adds the ngInvalid class,
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S… Speaker 1 (196. TD Using the Form State)
CSS class,
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to the form element.
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S… Speaker 1 (196. TD Using the Form State)
So a better approach would be to make sure that it is not
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S… Speaker 1 (196. TD Using the Form State)
added to the
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S… Speaker 1 (196. TD Using the Form State)
form now there are a couple of ways to doing this and it's all just pure
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S… Speaker 1 (196. TD Using the Form State)
css logic one idea would be that we want
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S… Speaker 1 (196. TD Using the Form State)
to be inside of the form element but then it would still place these
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S… Speaker 1 (196. TD Using the Form State)
red borders around grouping divs we will have a look at what i mean
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S… Speaker 1 (196. TD Using the Form State)
with this later so the best way is to simply be explicit
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S… Speaker 1 (196. TD Using the Form State)
that we want to add it on inputs for example
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S… Speaker 1 (196. TD Using the Form State)
And of course, you could also add select here.
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S… Speaker 1 (196. TD Using the Form State)
So input with ng -invalid or select with ng
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S… Speaker 1 (196. TD Using the Form State)
-invalid and which other elements you have.
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S… Speaker 1 (196. TD Using the Form State)
Just be creative here.
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S… Speaker 1 (196. TD Using the Form State)
There are different ways of achieving this goal.
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S… Speaker 1 (196. TD Using the Form State)
In the end, you just want to make sure that the border is applied to the right
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S… Speaker 1 (196. TD Using the Form State)
controls.
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S… Speaker 1 (196. TD Using the Form State)
Now with this in place,
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S… Speaker 1 (196. TD Using the Form State)
we see that now we only have a red border around the invalid controls,
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S… Speaker 1 (196. TD Using the Form State)
but we do have the border right from the start,
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which is also not great because
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S… Speaker 1 (196. TD Using the Form State)
I at least want to give the user the chance of changing it before showing
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a warning, showing that it's wrong.
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S… Speaker 1 (196. TD Using the Form State)
So a better approach might be to make sure that we only add a red border
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S… Speaker 1 (196. TD Using the Form State)
to an input which has the CSS class ng invalid and
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S… Speaker 1 (196. TD Using the Form State)
also the CSS class ng touched.
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S… Speaker 1 (196. TD Using the Form State)
So that user has to at least click into it.
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S… Speaker 1 (196. TD Using the Form State)
Now by default,
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S… Speaker 1 (196. TD Using the Form State)
we don't see anything red,
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S… Speaker 1 (196. TD Using the Form State)
even though the form is invalid.
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S… Speaker 1 (196. TD Using the Form State)
But if you click in there and decide,
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yeah, I'm done,
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S… Speaker 1 (196. TD Using the Form State)
this is my value.
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S… Speaker 1 (196. TD Using the Form State)
Well,
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S… Speaker 1 (196. TD Using the Form State)
now you see we have a red border because now we had a chance of changing
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S… Speaker 1 (196. TD Using the Form State)
it. We didn't change it.
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S… Speaker 1 (196. TD Using the Form State)
It is invalid and we want to show this.
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S… Speaker 1 (196. TD Using the Form State)
And with that,
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S… Speaker 1 (196. TD Using the Form State)
we're taking advantage of this form state handled by Angular.
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S… Speaker 1 (196. TD Using the Form State)
We disable the button and we show a visual feedback to
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the user.
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S… Speaker 1 (196. TD Using the Form State)
now you could of course go much further you could also add a warning
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message below this input here for example and
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S… Speaker 1 (196. TD Using the Form State)
output please enter a valid value
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S… Speaker 1 (196. TD Using the Form State)
or be more precise than that of course and
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S… Speaker 1 (196. TD Using the Form State)
add
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S… Speaker 1 (196. TD Using the Form State)
ngif to conditionally show this if the input
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value is wrong.
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S… Speaker 1 (196. TD Using the Form State)
Well,
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S… Speaker 1 (196. TD Using the Form State)
this gives us one additional problem though.
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S… Speaker 1 (196. TD Using the Form State)
How do we determine whether this input here
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or this control here does hold a wrong value?
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S… Speaker 1 (196. TD Using the Form State)
We'll take a closer look in the next lecture.

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