Select specific component with javascript

[campopianoa]

Hi folks,

This question is due to my lack of JS knowledge.

If I have two components on a custom HTML form named text_area_1 and text_area_2, how would I reference only text_area_1 in a JS function (via call_js)?

If I do this:

<script>
function setColor(color) {
  var all_textareas = this.find("textarea");
  all_textareas.css("background-color", color);
}
</script>

of course all textareas get a red background. I would like to access a single Anvil component by name or some other unique identifier.

I have read nearly every JS-related post on the forum, and explored the JQuery docs but I still have not been able to piece together the correct syntax.

Any slight nudge in the right direction would be much appreciated.

Here is my working clone:
https://FCPWWQJO7VL2H4ZU.anvil.app/YM5N3MPYZINMJHH6GUN5EMTI

[stefano.menci]

I have never found an easy way. See here: Add the component name to the HTML tag

One workaround that I sometime use is to put text_area_1 inside a container together with a label, make the label invisible and set its text to "text_area_1" (or any other unique string). Then javascript will look for a label with the text "text_area_1", get its parent, then its sibling and start from there.
It ain’t pretty and it’s brittle: I don’t know if the HTML structure of the components will change, but that’s the best solution that I have found so far.

[campopianoa]

Oh I see!

I was wondering why I couldn’t find an example of this in my reading (at least one that made sense to me).

I am going to try your clever solution here.

I have already upvoted your FR. Others please do the same!

Add the component name to the HTML tag

Please add an attribute with the component name to the HTML tag containing the component. The attribute would make it easier to access HTML tags from Javascript. FR inspired here by @david.wylie

[stefano.menci]

I just remembered of another limitation of my approach: when you use it in a repeating panel the text in the label cannot be just a name like "text_area_1" because you would end up with many items with the same id.
In this case I add something unique like a random number to the name, which is the easy part. Then I need to pass the whole id to javascript, which depending on the context can be tricky.

[stucork]

So I spent quite a lot of time working on how to do this with the popover and hover/focus behaviour dependencies…

This was my methodology and how I came about it:

• call the js function from the init method of a Form or from a button click or wherever makes sense…

• use the component as an argument

• if we then take a look at the component with console.log(component) we can start to dive into its attributes and methods using chrome dev tools.

• the path of the html element is: component.v._anvil.element (note this is a jQuery object)

• (depending on the component you will get different html tags - so a link component gives the <a> tag, text_box gives you the input element, a button component gives the surrounding div)

Optional:

• if you wanted to send the same element back to python use component.v e.g. anvil.call(html_element, 'my_function', component.v)

Example below:

https://anvil.works/build#clone:SIXH2YXISGCZN3VS=KWOC3UBMEFM243P27RS7UEZU

The code in the example is:

js.call_js('make_component_red', self.label_2)
js.call_js('make_component_red', self.button_1)
js.call_js('make_component_red', self.link_1)

in Native Libraries

<script>

function make_component_red(component){
    var html_element = component.v._anvil.element // jQuery Object
    html_element.css('background','red')

    // optional - if you want to then send this element back to a python function
    anvil.call(html_element, 'i_am_red', component.v)
};
  
</script>

A method inside the HTML Form that the component belongs to…(i.e. not a Blank Panel Form)

  def i_am_red(self, component):
    print(f"component '{component.__name__}' is now red")

---

side note: since the html element of a button component: button_component.v._anvil.element is the div rather than the button element, I got into the habit of using:

if (component.v._anvil.element[0].classList.contains("anvil-button")) {
        var html_component = $(component.v._anvil.element[0].firstElementChild) 
        // jQuery Button object rather than the surrounding div
    }
else { var html_component = component.v._anvil.element}; // jQuery object

But I don’t think it’s really necessary for most use cases…

You could also do:

if (component.v._anvil.componentSpec.type == "Button") {
        var html_component = $(component.v._anvil.element[0].firstElementChild)
        // jQuery Button object rather than the surrounding div
    }
else { var html_component = component.v._anvil.element}; // jQuery object

which is prettier… But only anvil elements that are created in the designer have a js attribute componentSpec.
Elements that are created in code don’t seem to have a componentSpec attribute so the former code worked more generally… I found this out the hard way…

---

side side note - I’m sure this is a case of use with caution - it’s not documented and just the result of me hacking around - anything not documented might be liable to change - but then again - the popover dependency made it into the component library …

[campopianoa]

@stefano.menci and @stucork thank you very much for this insight and for the concrete examples.

This is on the edge of my understanding and so these suggestions give me a lot to learn from. I’m going to dig into this.

I really appreciate it.

[stucork]

Good luck @alcampopiano

You may have worked it out but just to add - in the example you wrote - the code to change text_area_1 might look something like:

def button_1_click(self, **event_args):
  js.call_js('setColor', 'red', self.text_area_1)

---

<script>
function setColor(color, component) {
  var html_element = component.v._anvil.element // jQuery Object
  html_element.css("background-color", color);
}
</script>

---

A quick note
component.v._anvil.element is a jQuery object (just realised) so I didn’t need to use $(html_element) earlier. - i’ll edit.

So anything jQuery like you can use component.v._anvil.element

To get to the Dom Element from the jQuery object (in order to do Vanilla Javascript) you’d want to use component.v._anvil.element[0].

var html_element = component.v._anvil.element // jQuery Object
console.log(html_element instanceof jQuery) // true
var dom_element =  component.v._anvil.element[0] // Dom Element
console.log(dom_element instanceof Element) // true

---

Also the console is definitely your friend here - this is what you get in chrome devtools when you you do console.log(component). And basically how I went about finding out all of this stuff. Plus a lot of stackoverflow!

[campopianoa]

Hey Stu,

You may have worked it out but just to add - in the example you wrote - the code to change text_area_1 might look something like:

Yes, thank you. I was able to work out this part out.

The rest I’m understanding slowly. Your posts here are so thorough that they will continue to be a helpful resource for me and others. Pure gold. Thank you very much.