Function mergeHostAttrs

packages/core/src/render3/util/attrs_utils.ts:112–144

(
  dst: TAttributes | null,
  src: TAttributes | null,
)

 * @param src `TAttributes` which should be appended to `dst`
 */
export function mergeHostAttrs(
  dst: TAttributes | null,
  src: TAttributes | null,
): TAttributes | null {
  if (src === null || src.length === 0) {
    // do nothing
  } else if (dst === null || dst.length === 0) {
    // We have source, but dst is empty, just make a copy.
    dst = src.slice();
  } else {
    let srcMarker: AttributeMarker = AttributeMarker.ImplicitAttributes;
    for (let i = 0; i < src.length; i++) {
      const item = src[i];
      if (typeof item === 'number') {
        srcMarker = item;
      } else {
        if (srcMarker === AttributeMarker.NamespaceURI) {
          // Case where we need to consume `key1`, `key2`, `value` items.
        } else if (
          srcMarker === AttributeMarker.ImplicitAttributes ||
          srcMarker === AttributeMarker.Styles
        ) {
          // Case where we have to consume `key1` and `value` only.
          mergeHostAttribute(dst, srcMarker, item as string, null, src[++i] as string);
        } else {
          // Case where we have to consume `key1` only.
          mergeHostAttribute(dst, srcMarker, item as string, null, null);
        }
      }
    }
  }
  return dst;
}

/**
 * Append `key`/`value` to existing `TAttributes` taking region marker and duplicates into account.