解决方案

 //创建一个地图
let map = new BMapGL.Map("container");
//这里还需定位下位置，这里就不详细说明了，官方文档有示例
//开启鼠标滚轮缩放功能。仅对PC上有效
map.enableScrollWheelZoom(true);
//滚动开始触发事件，可通过map.getZoom() 获取缩放比例
map.addEventListener("zoomstart", function (e) {console.log(e.target.zoomLevel.toFixed(2));
});
//滚动动画及 步进入 触发事件 此事件在 zoomend 后 还会触发 ,不建议在此处进行任何操作，该位置仅做测试
map.addEventListener("zoom_changed", function (e) {console.log(e.target.zoomLevel.toFixed(2));
});
//滚动结束触发事件，如不想频繁触发，可通过节流函数控制
map.addEventListener("zoomend", function (e) {console.log(e.target.zoomLevel.toFixed(2));
});
//滚动动画开始时触发，在zoomstart事件后执行  
map.addEventListener("animation_start", function (e) {//加try 的原因 该方法不是zoom 唯一所有try {//zoom 包含三个参数 current 当前缩放比例 ，target 目标缩放比例  diff 比例差值let _zoom = this._animationInfo.zoom;//绝对值验证 放大 还是 缩小 //0.75 是为了防止 缩放控件 +1 -1 或其他缩放方法影响 if (!(Math.abs(_zoom.diff) > 0.75)) {// o.5 步进值if (_zoom.diff > 0) {this._animationInfo.zoom.diff = 0.5;} else {this._animationInfo.zoom.diff = -0.5;}this._animationInfo.zoom.current = _zoom.current;//改变目标值this._animationInfo.zoom.target = _zoom.current + this._animationInfo.zoom.diff;}} catch (error) {}
});

源码分析

//动画触发事件
_startInfiniteZoomAnimation: function(t) {var e = this;e._ani && e._ani.stop(!!t.goToEnd, {stopCurrentAnimation: t.stopCurrentAnimation}),e._infiniteAni || (this.fire(new aB("onanimation_start")),e._infiniteAni = new l({duration: 1e4,transition: bq.linear,render: function() {//步进值var i = e._animationInfo.zoom;return Math.abs(i.current - i.target) < .001 ? (e._setValue("zoom", i.target),void e._infiniteAni.stop()) : (i.current += .35 * (i.target - i.current),e._setValue("zoom", i.current),void (t.renderCallback && t.renderCallback()))},finish: function() {e._infiniteAni = null,e._animationInfo = {},e.fire(new aB("onanimation_end")),t.callback && t.callback()},onStop: function() {e._infiniteAni = null,e._animationInfo = {},e.fire(new aB("onanimation_end")),t.callback && t.callback()}}))
}

// zoom_changed 触发事件
_setValue: function (e, T) {if (e === "zoom") {this._preZoomLevel = this.zoomLevel;var i = this._getProperZoom(T);T = i.zoom;if (T !== this.zoomLevel) {this.zoomLevel = T;if (T < 5) {this.restrictCenter(this.centerPoint)}this.fire(new fS("on" + e + "_changed"))}return} else {if (e === "center") {this.centerPoint = T}}this["_" + e] = T;this.fire(new fS("on" + e + "_changed"))
}