我正在使用Google地图计算票价,在CoffeeScript中创建一个库。
初始化地图时如下:
var viewport = document.getElementById('viewport'),
options = {
center: new google.maps.LatLng(-34.397, 150.644),
zoom: 8
};
google.maps.event.addDomListener(window, 'load', function()
{
var map = new google.maps.Map(viewport, options);
});
按预期加载。
但是当我使用我的库初始化它时:
var viewport = document.getElementById('viewport'),
options = {
center: new google.maps.LatLng(-34.397, 150.644),
zoom: 8
},
map = new FareJS.Map(viewport, options);
视口保持灰色,移动地图会显示TypeError: a is undefined
。
经过一番研究后,我发现@opt
类中方法initializeMap
中Map
的值未定义。我发现这很奇怪,因为我在构造函数中设置它。陌生人仍然是@viewport
不未定义...只是@opt
。
有问题的课程是
class Map
constructor: (@viewport, @opt) ->
if not window.hasOwnProperty('google')
throw "Google Maps API could not be found, are you sure you installed it?"
@loadMapOnLoad()
initializeMap: () ->
@map = new google.maps.Map(@viewport, @opt)
return
loadMapOnLoad: () ->
google.maps.event.addDomListener(window, 'load', @initializeMap)
return
编译的内容如下:
var Map;
Map = (function() {
function Map(viewport, opt) {
this.viewport = viewport;
this.opt = opt;
if (!window.hasOwnProperty('google')) {
throw "Google Maps API could not be found, are you sure you installed it?";
}
this.loadMapOnLoad();
}
Map.prototype.initializeMap = function() {
this.map = new google.maps.Map(this.viewport, this.opt);
};
Map.prototype.loadMapOnLoad = function() {
google.maps.event.addDomListener(window, 'load', this.initializeMap);
};
return Map;
})();
为什么要这样做以及如何解决?
答案 0 :(得分:3)
问题是initializeMap
将在您的类/对象的上下文之外执行。 this
不会引用initializeMap
中的类实例。您必须执行以下操作之一:
# explicitly bind to @
# https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind
google.maps.event.addDomListener window, 'load', @initializeMap.bind @
# preserve context with => and call regularly
google.maps.event.addDomListener window, 'load', => @initializeMap()
# declare method with bound context, so it doesn't matter how you call it
# (resulting behaviour could be considered somewhat unidiomatic for JS, caveat emptor)
class Map
initializeMap: =>
..