更新 - 添加示例

您是否尝试过backbone.js库？通过添加模型和扩展，它将使Javascript代码更易于管理。结构。虽然有一个学习曲线，但它真的很棒。学习Backbone后，您可以使用 Backbone Forms 插件，这将有助于下拉管理。以下是演示链接&示例代码：

Have you try backbone.js library? It will make the Javascript code more manageable by adding models & structures. There is a learning curve though but it is really great. Once you learn Backbone, you can make use of the Backbone Forms plugin which will help in the dropdown management. Below is the demo link & sample code:

示例1

$(function() {
var cities = {
    'UK': ['London', 'Manchester', 'Brighton', 'Bristol'],
    'USA': ['London', 'Los Angeles', 'Austin', 'New York']
};

var subAreas = {
    'London' : ['L1', 'L2', 'L3', 'L4'],
    'Manchester' : ['M1', 'M2', 'M3', 'M4'],
    'Brighton' : ['B1', 'B2', 'B3', 'B4'],
    'Bristol' : ['BR1', 'BR2', 'BR3', 'BR4'],
    'Los Angeles' : ['LA1', 'LA2', 'LA3', 'LA4'],
    'Austin' : ['A1', 'A2', 'A3', 'A4'],
    'New York' : ['NY1', 'NY2', 'NY3', 'NY4']
};


//The form
var form = new Backbone.Form({
    schema: {
        country: { type: 'Select', options: ['UK', 'USA'] },
        city: { type: 'Select', options: cities.UK },
        subArea: { type: 'Select', options: subAreas[cities.UK[0] ] }
    }
}).render();

form.on('country:change', function(form, countryEditor) {
    var country = countryEditor.getValue(),
        newOptions = cities[country];

    form.fields.city.editor.setOptions(newOptions);

    var city = newOptions[0],
        areaOptions = subAreas[city];

    form.fields.subArea.editor.setOptions(areaOptions);

});

form.on('city:change', function(form, cityEditor) {
    var city = cityEditor.getValue(),
        newOptions = subAreas[city];

    form.fields.subArea.editor.setOptions(newOptions);
});

//Add it to the page
$('body').append(form.el);

}）;

示例2

$(function() {
var cities = {
    'UK': ['London', 'Manchester', 'Brighton', 'Bristol'],
    'USA': ['London', 'Los Angeles', 'Austin', 'New York']
};

var subAreas = {
    'UK.London' : ['L1', 'L2'],
    'USA.London' : ['L3', 'L4'],
    'UK.Manchester' : ['M1', 'M2', 'M3', 'M4'],
    'UK.Brighton' : ['B1', 'B2', 'B3', 'B4'],
    'UK.Bristol' : ['BR1', 'BR2', 'BR3', 'BR4'],
    'USA.Los Angeles' : ['LA1', 'LA2', 'LA3', 'LA4'],
    'USA.Austin' : ['A1', 'A2', 'A3', 'A4'],
    'USA.New York' : ['NY1', 'NY2', 'NY3', 'NY4']
};

var hashFunc = function(country, city){
    return country + "." + city;
};


//The form
var form = new Backbone.Form({
    schema: {
        country: { type: 'Select', options: ['UK', 'USA'] },
        city: { type: 'Select', options: cities.UK },
        subArea: { type: 'Select', options: subAreas[ 'UK.London' ] }
    }
}).render();

form.on('country:change', function(form, countryEditor) {
    var country = countryEditor.getValue(),
        newOptions = cities[country];

    form.fields.city.editor.setOptions(newOptions);

    var city = newOptions[0],
        areaOptions = subAreas[hashFunc(country, city) ];

    form.fields.subArea.editor.setOptions(areaOptions);

});

form.on('city:change', function(form, cityEditor) {

    var city = cityEditor.getValue(),
        newOptions = subAreas[hashFunc(form.getValue().country, city)];

    form.fields.subArea.editor.setOptions(newOptions);
});

//Add it to the page
$('body').append(form.el);
});​

当您还开发移动设备（可能是Phonegap）时，您可以也尝试使用ZeptoJS作为jQuery的替代品。它会提高速度。

As you also develop for mobile (probably Phonegap), you can also try ZeptoJS as an alternative for jQuery. It will improve the speed alot.