localstorage：获取包含许多项的特定localstorage值

Question

在本地存储中，我使用值键<'strong>结果'：

[{"id":"item-1","href":"google.com","icon":"google.com"},
{"id":"item-2","href":"youtube.com","icon":"youtube.com"},
{"id":"item-3","href":"google.com","icon":"google.com"},
{"id":"item-4","href":"google.com","icon":"google.com"},
{"id":"item-5","href":"youtube.com","icon":"youtube.com"},
{"id":"item-6","href":"asos.com","icon":"asos.com"},
{"id":"item-7","href":"google.com","icon":"google.com"},
{"id":"item-8","href":"mcdonalds.com","icon":"mcdonalds.com"}]

要获得我使用的最后一项：

// this is how I parse the arrays
var result = JSON.parse(localStorage.getItem("result")); 


for(var i=0;i<result.length;i++) {
    var item = result[i];
    $('element').val(item.href);
}

如何获取第3项或特定ID的href？

Answer 1

使用原生Array.filter

如果您只定位现代浏览器（IE9 +或任何其他主要浏览器的recent version），则可以使用JavaScript 1.6数组方法filter。

var testItem,
    data = [{"id":"item-1","href":"google.com","icon":"google.com"},
{"id":"item-2","href":"youtube.com","icon":"youtube.com"},
{"id":"item-3","href":"google.com","icon":"google.com"},
{"id":"item-4","href":"google.com","icon":"google.com"},
{"id":"item-5","href":"youtube.com","icon":"youtube.com"},
{"id":"item-6","href":"asos.com","icon":"asos.com"},
{"id":"item-7","href":"google.com","icon":"google.com"},
{"id":"item-8","href":"mcdonalds.com","icon":"mcdonalds.com"}];

function getItemById(data, id) {
    // filter array down to only the item that has the id
    // https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/filter
    var ret = data.filter(function (item) {
        return item.id === id;
    });

    // Return the first item from the filtered array   
    // returns undefined if item was not found
    return ret[0];
}


testItem = getItemById(data, 'item-3');

Working example

手动循环数据

如果你不能使用过滤器，你可能只是使用一个循环：

var testItem,
    data = [{"id":"item-1","href":"google.com","icon":"google.com"},
{"id":"item-2","href":"youtube.com","icon":"youtube.com"},
{"id":"item-3","href":"google.com","icon":"google.com"},
{"id":"item-4","href":"google.com","icon":"google.com"},
{"id":"item-5","href":"youtube.com","icon":"youtube.com"},
{"id":"item-6","href":"asos.com","icon":"asos.com"},
{"id":"item-7","href":"google.com","icon":"google.com"},
{"id":"item-8","href":"mcdonalds.com","icon":"mcdonalds.com"}];

function getItemById(data, id) {
    var i, len;
    for (i = 0, len = data.length; i < len; i += 1) {
        if(id === data[i].id) {
            return data[i];
        }
    }

    return undefined;
}

testItem = getItemById(data, 'item-3');

Working example

即使使用循环强制它可能看起来不如使用Array.filter那么优雅，但事实证明在大多数情况下loop is faster than Array.filter。

重构为对象而不是数组

假设每个项目的id都是唯一的，那么最好的解决方案就是重构您存储数据的方式。使用id作为键来存储包含href和icon键/属性值的对象的对象，而不是对象数组。

var data = {
    "item-1": {"href": "google.com", "icon": "google.com"},
    "item-2": {"href": "youtube.com", "icon": "youtube.com"},
    "item-3": {"href": "google.com", "icon": "google.com"},
    "item-4": {"href": "google.com", "icon": "google.com"},
    "item-5": {"href": "youtube.com", "icon": "youtube.com"},
    "item-6": {"href": "asos.com", "icon": "asos.com"},
    "item-7": {"href": "google.com", "icon": "google.com"},
    "item-8": {"href": "mcdonalds.com", "icon": "mcdonalds.com"}
};

这样可以更轻松，更快捷地访问项目：

var data = JSON.parse(localStorage.getItem("result")); 
data["item-3"].href;

Answer 2

jQuery有过滤器助手：

$(result).filter(function(){return this.id == "item-3";})[0]

具有特定id的项目的href函数将是：

function getItemHrefById(json, itemId){
    return json.filter(function(testItem){return testItem.id == itemId;})[0].href;
}

样本用法是：

var href = getItemHrefById(result, "item-3");

您可以在http://jsfiddle.net/LXvLB/

上查看工作示例

<强>更新

如果您无法从本地存储中读取项目，可能在设置值时忘记调用JSON.stringify：

localStorage["results"] = JSON.stringify([{"id":"item-1","href":"google.com","icon":"google.com"}, 
{"id":"item-2","href":"youtube.com","icon":"youtube.com"}, 
{"id":"item-3","href":"google.com","icon":"google.com"}, 
{"id":"item-4","href":"google.com","icon":"google.com"}, 
{"id":"item-5","href":"youtube.com","icon":"youtube.com"}, 
{"id":"item-6","href":"asos.com","icon":"asos.com"}, 
{"id":"item-7","href":"google.com","icon":"google.com"}, 
{"id":"item-8","href":"mcdonalds.com","icon":"mcdonalds.com"}])

您需要将json转换为字符串才能正确序列化（并使用JSON.parse来获取JSON）

This是最后的例子。

修改

正如无用代码指出的那样，这个方法比本机过滤器功能慢得多（和自定义循环，但我认为引入几行新代码来节省20-30ms是不合适的，除非性能是个问题），所以我是更新我的示例不使用jquery过滤器。请为他的答案+1。

此外，重要的是要指出，如果这个数组有数百个而不是8个书签，for循环可能在统计上大约快两倍（因为它不必遍历数组的其余部分）。但是，在这种情况下，将循环放入函数可能是一个好主意，该函数返回满足条件的第一个找到的项，并且使用prototypejs它甚至可以连接到数组。

Answer 3

对于jquery过滤器方法，我认为使用回调函数，并且绑定搜索参数更优雅和可读：

function filterById(id, i, obj) {
    return obj.id === id;
}

function getItemHrefById(json, itemId) {
    return $(json).filter(filterById.bind(null, itemId))[0].href;
}

da usual fiddle

（但是，我更喜欢“for loop”方法“为此!!）