deviceorientation

deviceorientation 事件在方向传感器输出新数据的时候触发。其数据系传感器与地球坐标系相比较所得，也就是说在设备上可能会采用设备地磁计的数据。详情参考有关方向与运动信息的说明（Orientation and motion data explained）。

常规信息

标准: Orientation
接口: DeviceOrientationEvent
冒泡: 否
可取消: 否
Target: DefaultView (window)
默认操作: 无

属性

Property	Type	Description
`target` 只读	`EventTarget`	The event target (the topmost target in the DOM tree).
`type` 只读	`DOMString`	The type of event.
`bubbles` 只读	`Boolean`	Whether the event normally bubbles or not
`cancelable` 只读	`Boolean`	Whether the event is cancellable or not?
`alpha` 只读	double (float)	The current orientation of the device around the Z axis; that is, how far the device is rotated around a line perpendicular to the device.
`beta` 只读	double (float)	The current orientation of the device around the X axis; that is, how far the device is tipped forward or backward.
`gamma` 只读	double (float)	The current orientation of the device around the Y axis; that is, how far the device is turned left or right.
`absolute` 只读	`boolean`	This value is `true` if the orientation is provided as a difference between the device coordinate frame and the Earth coordinate frame; if the device can't detect the Earth coordinate frame, this value is `false`.

例子

if (window.DeviceOrientationEvent) {
    window.addEventListener("deviceorientation", function(event) {
        // alpha: 在Z轴上的角度
        var rotateDegrees = event.alpha;
        // gamma: 从左到右
        var leftToRight = event.gamma;
        // beta: 从前到后的运动
        var frontToBack = event.beta;

        handleOrientationEvent(frontToBack, leftToRight, rotateDegrees);
    }, true);
}

var handleOrientationEvent = function(frontToBack, leftToRight, rotateDegrees) {
    // 弹奏一曲夏威夷吉他
};

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