我用原型链来写一个省市区联动的方法，我将变量放进初始的函数中，以便我用原型链拓展时使用。初始化时没问题的，但是在我用onchange选择省或者市时就出问题了，selectProvince和selectCity的属性options找不到，我在往上查找了一下，发现selectProvince和selectCity在用onchange时根本没有检测到，我明明在AddressInit里面初始化了，但却没检测到，求解？
代码：
//这是一小段的json

var provinceList = [{ name: '北京', cityList: [{ name: '市辖区', areaList: ['东城区', '西城区', '崇文区', '宣武区', '朝阳区', '丰台区', '石景山区', '海淀区', '门头沟区', '房山区', '通州区', '顺义区', '昌平区', '大兴区', '怀柔区', '平谷区'] }, { name: '县', areaList: ['密云县', '延庆县'] }] }];

//这是html

//这是js

var AddressInit = function(selectProvince, selectCity, selectArea, defaultProvince, defaultCity, defaultArea){ this.selectProvince = document.getElementById(selectProvince); this.selectCity = document.getElementById(selectCity); this.selectArea = document.getElementById(selectArea); this.defaultProvince = defaultProvince || ''; this.defaultCity = defaultCity || ''; this.defaultArea = defaultArea || ''; } AddressInit.prototype = { constructor: AddressInit, //初始化 init: function(){ for (var i = 0; i < provinceList.length; i++) { this.selectAddOption(this.selectProvince, provinceList[i].name, provinceList[i]); } this.selected(this.selectProvince, this.defaultProvince); this.changeProvince(); this.selectProvince.onchange = this.changeProvince; }, //判断是否有选中的值 selected: function(select,str){ for(var i = 0; i < select.options.length; i++) { if (select.options[i].value == str) { select.selectedIndex = i; return; } } }, //添加option selectAddOption: function(select, str, obj) { var option = document.createElement("option"); select.options.add(option); option.innerText = str; option.value = str; option.obj = obj; }, //改变省 changeProvince: function(){ console.log(selectCity); this.selectCity.options.length = 0; this.selectCity.onchange = null; if (this.selectProvince.selectedIndex == -1) return; var item = this.selectProvince.options[this.selectProvince.selectedIndex].obj; for (var i = 0; i < item.cityList.length; i++) { this.selectAddOption(this.selectCity, item.cityList[i].name, item.cityList[i]); } this.selected(this.selectCity, this.defaultCity); this.changeCity(); this.selectCity.onchange = this.changeCity; }, //改变市 changeCity: function(){ this.selectArea.options.length = 0; if (this.selectCity.selectedIndex == -1) return; var item = this.selectCity.options[this.selectCity.selectedIndex].obj; for (var i = 0; i < item.areaList.length; i++) { this.selectAddOption(this.selectArea, item.areaList[i], null); } this.selected(this.selectArea, this.defaultArea); } } var ccc = new AddressInit('selectProvince', 'selectCity', 'selectArea'); ccc.init();