Submitting a form using a custom button using HTML Web Components - html

Question

I have defined a custom DOM element, but when placed inside a form, it does not submit it. How can I get the form to submit when I click the button?
<form action="/foo" method="GET">
<my-button type="submit">click me</my-button>
</form>
This is the prototype configuration for the custom element:
myButton = Object.create(HTMLButtonElement.prototype);
The template for the button looks like this:
<template>
<button type="submit" id="button"><content></content></button>
</template>

Answer 1

Came across this question today, but found a more modern alternative subsequently: web components can now be native form elements. There's a great read on the topic here.
The long and the short of it is you can now associate custom components with a form, meaning they're included in the form's elements property - a HTMLFormControlsCollection of all the elements controlled by the form.
To do this, you need to add the following to your component:
class MyComponent extends HTMLElement {
static get formAssociated() { return true; }
constructor() {
super();
this.internals = this.attachInternals();
}
}
this.internals will then contain everything you need to interact with the form in question, e.g. this.internals.form, this.internals.setFormValue(), this.internals.checkValidity().
For the submit button, you could, for example, use:
connectedCallback() {
const { internals: { form } } = this;
this.buttonEl.addEventListener('click', () => form.submit());
}

Answer 2

You are doing it wrong. Though event bubbling from shadow DOM to owner document is somehow possible, it’s tricky and in general is a wrong approach. Instead of hiding button into shadow, one should use is= attribute of button:
<form action="/foo" method="GET">
<!--my-button type="submit">click me</my-button-->
<!-- ⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓ -->
<button type="submit" is="my-button">click me</button>
</form>
More info.

Answer 3

When your custom element extends a native element like HTMLButtonElement, you can no longer use a custom tag name like <my-button> (unfortunately). You have to use the native tag with the is= attribute:
<button type="submit" is="my-button">
If you do not extend a native element (called "type extension" in the spec), then you can use your custom tag name. Type extension example in the spec