Function findStylingValue

packages/core/src/render3/instructions/styling.ts:946–1004

* Search for styling value with higher priority which is overwriting current value, or a * value of lower priority to which we should fall back if the value is `undefined`. * * When value is being applied at a location, related values need to be consulted. * - If there is a higher priority bindi

(
  tData: TData,
  tNode: TNode | null,
  lView: LView,
  prop: string,
  index: number,
  isClassBased: boolean,
)

 * @param isClassBased `true` if `class` (`false` if `style`)
 */
function findStylingValue(
  tData: TData,
  tNode: TNode | null,
  lView: LView,
  prop: string,
  index: number,
  isClassBased: boolean,
): any {
  // `TNode` to use for resolving static styling. Also controls search direction.
  //   - `TNode` search next and quit as soon as `isStylingValuePresent(value)` is true.
  //      If no value found consult `tNode.residualStyle`/`tNode.residualClass` for default value.
  //   - `null` search prev and go all the way to end. Return last value where
  //     `isStylingValuePresent(value)` is true.
  const isPrevDirection = tNode === null;
  let value: any = undefined;
  while (index > 0) {
    const rawKey = tData[index] as TStylingKey;
    const containsStatics = Array.isArray(rawKey);
    // Unwrap the key if we contain static values.
    const key = containsStatics ? (rawKey as string[])[1] : rawKey;
    const isStylingMap = key === null;
    let valueAtLViewIndex = lView[index + 1];
    if (valueAtLViewIndex === NO_CHANGE) {
      // In firstUpdatePass the styling instructions create a linked list of styling.
      // On subsequent passes it is possible for a styling instruction to try to read a binding
      // which
      // has not yet executed. In that case we will find `NO_CHANGE` and we should assume that
      // we have `undefined` (or empty array in case of styling-map instruction) instead. This
      // allows the resolution to apply the value (which may later be overwritten when the
      // binding actually executes.)
      valueAtLViewIndex = isStylingMap ? EMPTY_ARRAY : undefined;
    }
    let currentValue = isStylingMap
      ? keyValueArrayGet(valueAtLViewIndex, prop)
      : key === prop
        ? valueAtLViewIndex
        : undefined;
    if (containsStatics && !isStylingValuePresent(currentValue)) {
      currentValue = keyValueArrayGet(rawKey as KeyValueArray<any>, prop);
    }
    if (isStylingValuePresent(currentValue)) {
      value = currentValue;
      if (isPrevDirection) {
        return value;
      }
    }
    const tRange = tData[index + 1] as TStylingRange;
    index = isPrevDirection ? getTStylingRangePrev(tRange) : getTStylingRangeNext(tRange);
  }
  if (tNode !== null) {
    // in case where we are going in next direction AND we did not find anything, we need to
    // consult residual styling
    let residual = isClassBased ? tNode.residualClasses : tNode.residualStyles;
    if (residual != null /** OR residual !=== undefined */) {
      value = keyValueArrayGet(residual!, prop);
    }
  }
  return value;