`TNode.directives` was introduced in https://github.com/angular/angular/pull/34938. Turns out that it is unnecessary because the information is already present it `TData` when combining with `TNode.directiveStart` and `TNode.directiveEnd`
Mainly this is true (conceptually):
```
expect(tNode.directives).toEqual(
tData.slice(
tNode.directivesStart,
tNode.directivesEnd - tNode.DirectivesStart -1
)
);
```
The refactoring removes `TNode.directives` and adds `TNode.directiveStyling` as we still need to keep location in the directive in `TNode`
PR Close#35050
This change changes the priority order of static styling.
Current priority:
```
(least priority)
- Static
- Component
- Directives
- Template
- Dynamic Binding
- Component
- Map/Interpolation
- Property
- Directives
- Map/Interpolation
- Property
- Template
- Map/Interpolation
- Property
(highest priority)
```
The issue with the above priority is this use case:
```
<div style="color: red;" directive-which-sets-color-blue>
```
In the above case the directive will win and the resulting color will be `blue`. However a small change of adding interpolation to the example like so. (Style interpolation is coming in https://github.com/angular/angular/pull/34202)
```
<div style="color: red; width: {{exp}}px" directive-which-sets-color-blue>
```
Changes the priority from static binding to interpolated binding which means now the resulting color is `red`. It is very surprising that adding an unrelated interpolation and style can change the `color` which was not changed. To fix that we need to make sure that the static values are associated with priority of the source (directive or template) where they were declared. The new resulting priority is:
```
(least priority)
- Component
- Static
- Map/Interpolation
- Property
- Directives
- Static
- Map/Interpolation
- Property
- Template
- Static
- Map/Interpolation
- Property
(highest priority)
```
PR Close#34938
Previously we would write to class/style as strings `element.className` and `element.style.cssText`. Turns out that approach is good for initial render but not good for updates. Updates using this approach are problematic because we have to check to see if there was an out of bound write to style and than perform reconciliation. This also requires the browser to bring up CSS parser which is expensive.
Another problem with old approach is that we had to queue the DOM writes and flush them twice. Once on element advance instruction and once in `hostBindings`. The double flushing is expensive but it also means that a directive can observe that styles are not yet written (they are written after directive executes.)
The new approach uses `element.classList.add/remove` and `element.style.setProperty/removeProperty` API for updates only (it continues to use `element.className` and `element.style.cssText` for initial render as it is cheaper.) The other change is that the styling changes are applied immediately (no queueing). This means that it is the instruction which computes priority. In some circumstances it may result in intermediate writes which are than overwritten with new value. (This should be rare)
Overall this change deletes most of the previous code and replaces it with new simplified implement. The simplification results in code savings.
PR Close#34804
NOTE: This change must be reverted with previous deletes so that it code remains in build-able state.
This change deletes old styling code and replaces it with a simplified styling algorithm.
The mental model for the new algorithm is:
- Create a linked list of styling bindings in the order of priority. All styling bindings ere executed in compiled order and than a linked list of bindings is created in priority order.
- Flush the style bindings at the end of `advance()` instruction. This implies that there are two flush events. One at the end of template `advance` instruction in the template. Second one at the end of `hostBindings` `advance` instruction when processing host bindings (if any).
- Each binding instructions effectively updates the string to represent the string at that location. Because most of the bindings are additive, this is a cheap strategy in most cases. In rare cases the strategy requires removing tokens from the styling up to this point. (We expect that to be rare case)S Because, the bindings are presorted in the order of priority, it is safe to resume the processing of the concatenated string from the last change binding.
PR Close#34616
Misko Hevery