angularjs 源码解析之scope(4)

function $watchCollectionInterceptor(_value) { newValue = _value; var newLength, key, bothNaN, newItem, oldItem; if (isUndefined(newValue)) return; if (!isObject(newValue)) { if (oldValue !== newValue) { oldValue = newValue; changeDetected++; } } else if (isArrayLike(newValue)) { if (oldValue !== internalArray) { oldValue = internalArray; oldLength = oldValue.length = 0; changeDetected++; } newLength = newValue.length; if (oldLength !== newLength) { changeDetected++; oldValue.length = oldLength = newLength; } for (var i = 0; i < newLength; i++) { oldItem = oldValue[i]; newItem = newValue[i]; bothNaN = (oldItem !== oldItem) && (newItem !== newItem); if (!bothNaN && (oldItem !== newItem)) { changeDetected++; oldValue[i] = newItem; } } } else { if (oldValue !== internalObject) { oldValue = internalObject = {}; oldLength = 0; changeDetected++; } newLength = 0; for (key in newValue) { if (hasOwnProperty.call(newValue, key)) { newLength++; newItem = newValue[key]; oldItem = oldValue[key]; if (key in oldValue) { bothNaN = (oldItem !== oldItem) && (newItem !== newItem); if (!bothNaN && (oldItem !== newItem)) { changeDetected++; oldValue[key] = newItem; } } else { oldLength++; oldValue[key] = newItem; changeDetected++; } } } if (oldLength > newLength) { changeDetected++; for (key in oldValue) { if (!hasOwnProperty.call(newValue, key)) { oldLength--; delete oldValue[key]; } } } } return changeDetected; }

1). 当值为undefined时直接返回。

2). 当值为普通基本类型时 直接判断是否相等。

3). 当值为类数组 （即存在 length 属性，并且 value[i] 也成立称为类数组），先没有初始化先初始化oldValue

if (oldValue !== internalArray) { oldValue = internalArray; oldLength = oldValue.length = 0; changeDetected++; }

然后比较数组长度，不等的话记为已变化 changeDetected++

if (oldLength !== newLength) { changeDetected++; oldValue.length = oldLength = newLength; }

再进行逐个比较

for (var i = 0; i < newLength; i++) { oldItem = oldValue[i]; newItem = newValue[i]; bothNaN = (oldItem !== oldItem) && (newItem !== newItem); if (!bothNaN && (oldItem !== newItem)) { changeDetected++; oldValue[i] = newItem; } }

4). 当值为object时，类似上面进行初始化处理

if (oldValue !== internalObject) { oldValue = internalObject = {}; oldLength = 0; changeDetected++; }

接下来的处理比较有技巧，但凡发现 newValue 多的新字段，就在oldLength 加1，这样 oldLength 只加不减，很容易发现 newValue 中是否有新字段出现，最后把 oldValue中多出来的字段也就是 newValue 中删除的字段给移除就结束了。

newLength = 0; for (key in newValue) { if (hasOwnProperty.call(newValue, key)) { newLength++; newItem = newValue[key]; oldItem = oldValue[key]; if (key in oldValue) { bothNaN = (oldItem !== oldItem) && (newItem !== newItem); if (!bothNaN && (oldItem !== newItem)) { changeDetected++; oldValue[key] = newItem; } } else { oldLength++; oldValue[key] = newItem; changeDetected++; } } } if (oldLength > newLength) { changeDetected++; for (key in oldValue) { if (!hasOwnProperty.call(newValue, key)) { oldLength--; delete oldValue[key]; } } }

4.4 $watchCollectionAction

function $watchCollectionAction() { if (initRun) { initRun = false; listener(newValue, newValue, self); } else { listener(newValue, veryOldValue, self); } // trackVeryOldValue = (listener.length > 1) 查看listener方法是否需要oldValue // 如果需要就进行复制 if (trackVeryOldValue) { if (!isObject(newValue)) { veryOldValue = newValue; } else if (isArrayLike(newValue)) { veryOldValue = new Array(newValue.length); for (var i = 0; i < newValue.length; i++) { veryOldValue[i] = newValue[i]; } } else { veryOldValue = {}; for (var key in newValue) { if (hasOwnProperty.call(newValue, key)) { veryOldValue[key] = newValue[key]; } } } } }

代码还是比较简单，就是调用 listenerFn，初次调用时 oldValue == newValue，为了效率和内存判断了下 listener是否需要oldValue参数

5. $eval & $apply

$eval: function(expr, locals) { return $parse(expr)(this, locals); }, $apply: function(expr) { try { beginPhase('$apply'); return this.$eval(expr); } catch (e) { $exceptionHandler(e); } finally { clearPhase(); try { $rootScope.$digest(); } catch (e) { $exceptionHandler(e); throw e; } } }

$apply 最后调用 $rootScope.$digest()，所以很多书上建议使用 $digest() ，而不是调用 $apply()，效率要高点。

主要逻辑都在$parse 属于语法解析功能，后续单独分析。

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