Function mergeHostAttribute

packages/core/src/render3/util/attrs_utils.ts:155–221

(
  dst: TAttributes,
  marker: AttributeMarker,
  key1: string,
  key2: string | null,
  value: string | null,
)

 * @param value Value to add or to overwrite to `TAttributes` Only used if `marker` is not Class.
 */
export function mergeHostAttribute(
  dst: TAttributes,
  marker: AttributeMarker,
  key1: string,
  key2: string | null,
  value: string | null,
): void {
  let i = 0;
  // Assume that new markers will be inserted at the end.
  let markerInsertPosition = dst.length;
  // scan until correct type.
  if (marker === AttributeMarker.ImplicitAttributes) {
    markerInsertPosition = -1;
  } else {
    while (i < dst.length) {
      const dstValue = dst[i++];
      if (typeof dstValue === 'number') {
        if (dstValue === marker) {
          markerInsertPosition = -1;
          break;
        } else if (dstValue > marker) {
          // We need to save this as we want the markers to be inserted in specific order.
          markerInsertPosition = i - 1;
          break;
        }
      }
    }
  }

  // search until you find place of insertion
  while (i < dst.length) {
    const item = dst[i];
    if (typeof item === 'number') {
      // since `i` started as the index after the marker, we did not find it if we are at the next
      // marker
      break;
    } else if (item === key1) {
      // We already have same token
      if (key2 === null) {
        if (value !== null) {
          dst[i + 1] = value;
        }
        return;
      } else if (key2 === dst[i + 1]) {
        dst[i + 2] = value!;
        return;
      }
    }
    // Increment counter.
    i++;
    if (key2 !== null) i++;
    if (value !== null) i++;
  }

  // insert at location.
  if (markerInsertPosition !== -1) {
    dst.splice(markerInsertPosition, 0, marker);
    i = markerInsertPosition + 1;