function updateChildren()

in assets/modelRepository/vue.js [5951:6068]
108 lines of code
19 McCabe index (conditional complexity)

    function updateChildren(
      parentElm,
      oldCh,
      newCh,
      insertedVnodeQueue,
      removeOnly
    ) {
      let oldStartIdx = 0;
      let newStartIdx = 0;
      let oldEndIdx = oldCh.length - 1;
      let oldStartVnode = oldCh[0];
      let oldEndVnode = oldCh[oldEndIdx];
      let newEndIdx = newCh.length - 1;
      let newStartVnode = newCh[0];
      let newEndVnode = newCh[newEndIdx];
      let oldKeyToIdx, idxInOld, vnodeToMove, refElm;

      // removeOnly is a special flag used only by <transition-group>
      // to ensure removed elements stay in correct relative positions
      // during leaving transitions
      const canMove = !removeOnly;

      {
        checkDuplicateKeys(newCh);
      }

      while (oldStartIdx <= oldEndIdx && newStartIdx <= newEndIdx) {
        if (isUndef(oldStartVnode)) {
          oldStartVnode = oldCh[++oldStartIdx]; // Vnode has been moved left
        } else if (isUndef(oldEndVnode)) {
          oldEndVnode = oldCh[--oldEndIdx];
        } else if (sameVnode(oldStartVnode, newStartVnode)) {
          patchVnode(oldStartVnode, newStartVnode, insertedVnodeQueue);
          oldStartVnode = oldCh[++oldStartIdx];
          newStartVnode = newCh[++newStartIdx];
        } else if (sameVnode(oldEndVnode, newEndVnode)) {
          patchVnode(oldEndVnode, newEndVnode, insertedVnodeQueue);
          oldEndVnode = oldCh[--oldEndIdx];
          newEndVnode = newCh[--newEndIdx];
        } else if (sameVnode(oldStartVnode, newEndVnode)) {
          // Vnode moved right
          patchVnode(oldStartVnode, newEndVnode, insertedVnodeQueue);
          canMove &&
            nodeOps.insertBefore(
              parentElm,
              oldStartVnode.elm,
              nodeOps.nextSibling(oldEndVnode.elm)
            );
          oldStartVnode = oldCh[++oldStartIdx];
          newEndVnode = newCh[--newEndIdx];
        } else if (sameVnode(oldEndVnode, newStartVnode)) {
          // Vnode moved left
          patchVnode(oldEndVnode, newStartVnode, insertedVnodeQueue);
          canMove &&
            nodeOps.insertBefore(parentElm, oldEndVnode.elm, oldStartVnode.elm);
          oldEndVnode = oldCh[--oldEndIdx];
          newStartVnode = newCh[++newStartIdx];
        } else {
          if (isUndef(oldKeyToIdx)) {
            oldKeyToIdx = createKeyToOldIdx(oldCh, oldStartIdx, oldEndIdx);
          }
          idxInOld = isDef(newStartVnode.key)
            ? oldKeyToIdx[newStartVnode.key]
            : findIdxInOld(newStartVnode, oldCh, oldStartIdx, oldEndIdx);
          if (isUndef(idxInOld)) {
            // New element
            createElm(
              newStartVnode,
              insertedVnodeQueue,
              parentElm,
              oldStartVnode.elm,
              false,
              newCh,
              newStartIdx
            );
          } else {
            vnodeToMove = oldCh[idxInOld];
            if (sameVnode(vnodeToMove, newStartVnode)) {
              patchVnode(vnodeToMove, newStartVnode, insertedVnodeQueue);
              oldCh[idxInOld] = undefined;
              canMove &&
                nodeOps.insertBefore(
                  parentElm,
                  vnodeToMove.elm,
                  oldStartVnode.elm
                );
            } else {
              // same key but different element. treat as new element
              createElm(
                newStartVnode,
                insertedVnodeQueue,
                parentElm,
                oldStartVnode.elm,
                false,
                newCh,
                newStartIdx
              );
            }
          }
          newStartVnode = newCh[++newStartIdx];
        }
      }
      if (oldStartIdx > oldEndIdx) {
        refElm = isUndef(newCh[newEndIdx + 1])
          ? null
          : newCh[newEndIdx + 1].elm;
        addVnodes(
          parentElm,
          refElm,
          newCh,
          newStartIdx,
          newEndIdx,
          insertedVnodeQueue
        );
      } else if (newStartIdx > newEndIdx) {
        removeVnodes(parentElm, oldCh, oldStartIdx, oldEndIdx);
      }
    }