angularjs – ng-repeat如何工作？

我有很多问题,但由于它们都是关于ng-repeat的内部结构,所以我选择在这里问问它们.我认为没有理由将它们分成不同的SO问题.我已经在内联标记了每个问题引用的代码行.

>为什么他们需要确保trackById不是本机hasOwnProperty函数？ (这就是assertNotHasOwnProperty函数所做的,是Angular内部API的一部分)
>就我的直觉而言,这段代码会对已经在转发器中的项目执行,当它必须更新集合时 – 它只是将它们拾取并将它们推入列表进行处理,对吧？
>此代码块显然在转发器集合中查找重复项.但它究竟是如何做到这一点超出了我.请解释.
>为什么Angular必须将块对象存储在nextBlockMap和nextBlockOrder中？
>什么是block.endNode和block.startNode？
>我假设上述问题的答案将阐明该算法的工作原理,但请解释为什么必须检查nextNode是否已经’$$NG_REMOVED’？
>这里发生了什么？同样,我认为问题6已经为这一个提供了答案.但仍然指出了这一点.

就像我说的那样,我挖掘ng-repeat来找到我认为与重复机制相关的代码.另外,我完全理解指令的其余部分.所以不用多说,这里是代码(来自v1.2.0)：

length = nextBlockOrder.length = collectionKeys.length;
      for (index = 0; index < length; index++) {
       key = (collection === collectionKeys) ? index : collectionKeys[index];
       value = collection[key];
       trackById = trackByIdFn(key,value,index);

       // question #1
       assertNotHasOwnProperty(trackById,'`track by` id');

       // question #2
       if (lastBlockMap.hasOwnProperty(trackById)) {
         block = lastBlockMap[trackById];
         delete lastBlockMap[trackById];
         nextBlockMap[trackById] = block;
         nextBlockOrder[index] = block;

       // question #3
       } else if (nextBlockMap.hasOwnProperty(trackById)) {
         // restore lastBlockMap
         forEach(nextBlockOrder,function(block) {
           if (block && block.startNode) lastBlockMap[block.id] = block;
         });
         // This is a duplicate and we need to throw an error
         throw ngRepeatMinErr('dupes',"Duplicates in a repeater are not allowed. Use 'track by' expression to specify unique keys. Repeater: {0},Duplicate key: {1}",expression,trackById);

       // question #4
       } else {
         // new never before seen block
         nextBlockOrder[index] = { id: trackById };
         nextBlockMap[trackById] = false;
       }
     }


      for (index = 0,length = collectionKeys.length; index < length; index++) {
        key = (collection === collectionKeys) ? index : collectionKeys[index];
        value = collection[key];
        block = nextBlockOrder[index];


        // question #5
        if (nextBlockOrder[index - 1]) previousNode = nextBlockOrder[index - 1].endNode;

        if (block.startNode) {
          // if we have already seen this object,then we need to reuse the
          // associated scope/element
          childScope = block.scope;

          // question #6
          nextNode = previousNode;
          do {
            nextNode = nextNode.nextSibling;
          } while(nextNode && nextNode[NG_REMOVED]);
          if (block.startNode != nextNode) {
            // existing item which got moved
            $animate.move(getBlockElements(block),null,jqLite(previousNode));
          }
          previousNode = block.endNode;

        } else {
          // new item which we don't know about
          childScope = $scope.$new();
        }

        // question #7
        if (!block.startNode) {
          linker(childScope,function(clone) {
            clone[clone.length++] = document.createComment(' end ngRepeat: ' + expression + ' ');
            $animate.enter(clone,jqLite(previousNode));
            previousNode = clone;
            block.scope = childScope;
            block.startNode = previousNode && previousNode.endNode ? previousNode.endNode : clone[0];
            block.endNode = clone[clone.length - 1];
            nextBlockMap[block.id] = block;
          });
        }
      }
      lastBlockMap = nextBlockMap;