Use the connectedCallback function to set button styles instead of the constructor #55
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The test shows that changes to the `level` attribute of a markdown header button aren't reflected in the output when pressing the button.
Building a header button in memory with a custom heading ("level")
causes a unexpected behaviour. Consider the following example:
```js
const headerButton = document.createElement('md-header') // The constructor is executed at this point.
headerButton.setAttribute('level', '1') // Has no effect since the style has already been set.
headerButton.textContent = 'h1'
document.body.appendChild(headerButton)
```
While we expect to have a header button that outputs a single hash
(`#`), we have a button that outputs three (`###`). The constructor sets
the styles based on the `level` attribute when the component is
initialised.
Changing the constructor to a `connectedCallback` function
ensures that the button styles aren't set until the button is connected
to the DOM.
`constructor` will call the `super` function automatically. We don't have to allocate code to do that as well.
Since `constructor` can be error-prone for custom elements and keep all the components similar, I've also changed all the constructors to `connectedCallback` functions.
Even though we don't expect header buttons to change levels dynamically during an application lifetime, we should ensure that it works as expected. So I've added an `attributeChangedCallback` to the header button element. The callback changes the level style based on the `level` attribute.
theinterned
approved these changes
Jan 4, 2022
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Building a header button in memory with a custom heading ("level") causes a unexpected behaviour. Consider the following example:
While we expect to have a header button that outputs a single hash (
#), we have a button that outputs three (###). The constructor sets the styles based on thelevelattribute when the component is initialised. Changing the constructor to aconnectedCallbackfunction ensures that the button styles aren't set until the button is connected to the DOM.Since
constructorcan be error-prone for custom elements and keep all the components similar, I've also changed all the constructors toconnectedCallbackfunctions.Finally, even though we don't expect header buttons to change levels dynamically during an application lifetime, we should ensure that it works as expected. So I've added an
attributeChangedCallbackto the header button element. The callback changes the level style based on thelevelattribute.Fixes #40 and possibly #45