JavaScript for-in 语句

for-in 语句是一种精准的迭代语句，可以用来枚举对象的属性。以下是 for-in 语句的语法：

for (property in expression) statement

下面是在 QML 中的使用实例：

    Item {
        id: testItem

        Component.onCompleted: {
            // js start
            for (var propertyName in testItem ) {
                console.log("testItem's property name: ", propertyName.toString());
            }
            // js end
        }
    }

输出结果如下：

QML debugging is enabled. Only use this in a safe environment.
qml: testItem's property name:  objectName
qml: testItem's property name:  parent
qml: testItem's property name:  data
qml: testItem's property name:  resources
qml: testItem's property name:  children
qml: testItem's property name:  x
qml: testItem's property name:  y
qml: testItem's property name:  z
qml: testItem's property name:  width
qml: testItem's property name:  height
qml: testItem's property name:  opacity
qml: testItem's property name:  enabled
qml: testItem's property name:  visible
qml: testItem's property name:  visibleChildren
qml: testItem's property name:  states
qml: testItem's property name:  transitions
qml: testItem's property name:  state
qml: testItem's property name:  childrenRect
qml: testItem's property name:  anchors
qml: testItem's property name:  left
qml: testItem's property name:  right
qml: testItem's property name:  horizontalCenter
qml: testItem's property name:  top
qml: testItem's property name:  bottom
qml: testItem's property name:  verticalCenter
qml: testItem's property name:  baseline
qml: testItem's property name:  baselineOffset
qml: testItem's property name:  clip
qml: testItem's property name:  focus
qml: testItem's property name:  activeFocus
qml: testItem's property name:  activeFocusOnTab
qml: testItem's property name:  rotation
qml: testItem's property name:  scale
qml: testItem's property name:  transformOrigin
qml: testItem's property name:  transformOriginPoint
qml: testItem's property name:  transform
qml: testItem's property name:  smooth
qml: testItem's property name:  antialiasing
qml: testItem's property name:  implicitWidth
qml: testItem's property name:  implicitHeight
qml: testItem's property name:  layer
qml: testItem's property name:  destroyed
qml: testItem's property name:  destroyed
qml: testItem's property name:  objectNameChanged
qml: testItem's property name:  deleteLater
qml: testItem's property name:  _q_reregisterTimers
qml: testItem's property name:  childrenRectChanged
qml: testItem's property name:  baselineOffsetChanged
qml: testItem's property name:  stateChanged
qml: testItem's property name:  focusChanged
qml: testItem's property name:  activeFocusChanged
qml: testItem's property name:  activeFocusOnTabChanged
qml: testItem's property name:  parentChanged
qml: testItem's property name:  transformOriginChanged
qml: testItem's property name:  smoothChanged
qml: testItem's property name:  antialiasingChanged
qml: testItem's property name:  clipChanged
qml: testItem's property name:  windowChanged
qml: testItem's property name:  childrenChanged
qml: testItem's property name:  opacityChanged
qml: testItem's property name:  enabledChanged
qml: testItem's property name:  visibleChanged
qml: testItem's property name:  visibleChildrenChanged
qml: testItem's property name:  rotationChanged
qml: testItem's property name:  scaleChanged
qml: testItem's property name:  xChanged
qml: testItem's property name:  yChanged
qml: testItem's property name:  widthChanged
qml: testItem's property name:  heightChanged
qml: testItem's property name:  zChanged
qml: testItem's property name:  implicitWidthChanged
qml: testItem's property name:  implicitHeightChanged
qml: testItem's property name:  update
qml: testItem's property name:  _q_resourceObjectDeleted
qml: testItem's property name:  contains
qml: testItem's property name:  mapFromItem
qml: testItem's property name:  mapToItem
qml: testItem's property name:  forceActiveFocus
qml: testItem's property name:  forceActiveFocus
qml: testItem's property name:  nextItemInFocusChain
qml: testItem's property name:  nextItemInFocusChain
qml: testItem's property name:  childAt