Question

我在sessionStorage中有一个JavaScript数组，当我执行sessionStorage.getitem('states')时，我会这样：

"{
    "TamilNadu": [
        "Chennai", 
        "Trichy", 
        "Madurai"
    ],
    "Andhra": [
        "Hyderabad",
        "Vizhag"
    ],
    "Karnataka": [
        "Bangalore",
        "Mysore",
        "Darwad"
    ],
    "Maharashtra": [
        "Mumbai",
        "Pune"
    ]
}"

现在我的要求是从城市名称获取州名。例如，如果我将"Mumbai"作为参数传递给函数，则该函数应读取此sessionstorage值并返回"Maharashtra"。

你能帮我解决一下这个问题吗？

Answer 1

此代码：

sessionStorage.getitem('states')

返回一个字符串。你必须用：

解析它

var obj = JSON.parse(sessionStorage.getitem('states'))

下一个使用方括号或点访问对象属性：

for (var attr in obj) {
    if (obj.hasOwnProperty(attr) && obj[attr][0] == 'Mumbai') {
        return attr;
    }
}
return null;

Answer 2

function getStateByCityName (cityName) {
    var states = {};
    try {
        states = JSON.parse(sessionStorage.getitem('states'));
    } catch (e) {
    }
    for (var state in states) {
        for (var i = 0; i < states[state].length; i ++) {
            if (states[state][i] == cityName)
                return state;
        }
    }
    return null;
}

Answer 3

或者只使用if (states[state].indexOf(cityName) !== -1)

getStateByCityName(cityName) {
    var statesRaw = sessionStorage.getitem('states');
    var states = JSON.parse(statesRaw);
    for (var state in states) {
        if (states[state].indexOf(cityName) !== -1) {
            return state;
        }
    }
    return false;
}

或者在EcmaScript 5循环风格中：））

getStateByCityName(cityName) {
    var statesRaw = sessionStorage.getitem('states');
    var states = JSON.parse(statesRaw);

    Object.keys(states).forEach(function(state) {
        if (states[state].indexOf(cityName) !== -1) {
            return state;
        }
    })
    return false;
}

有很多方法（参见其他答案）所以让我们来看看性能。

首先迭代你的对象 http://jsperf.com/object-keys-vs-for-in-with-closure/3

在我的浏览器中，最快的案例是Object.keys for loop，所以

getStateByCityName(cityName) {
    var statesRaw = sessionStorage.getitem('states');
    var states = JSON.parse(statesRaw);
    var states_keys = Object.keys(states);

    for (var i = 0, l = states_keys.length; i < l; i++) {
          // check if city exists
    }
    return false;
}

接下来，我们需要检查该城市是否存在。我认为有两种方法可以做到： 1）正如其他人建议用for循环迭代 2）我的建议.indexOf()

http://jsperf.com/js-for-loop-vs-array-indexof/2 在我的浏览器中indexOf()得到了更好的结果，所以最后的功能

getStateByCityName(cityName) {
    var statesRaw = sessionStorage.getitem('states');
    var states = JSON.parse(statesRaw);
    var states_keys = Object.keys(states);

    for (var i = 0, l = states_keys.length; i < l; i++) {
        if (states[states_keys[i]].indexOf(cityName) !== -1) {
            return states_keys[i];
        }
    }
    return false;
}

正如有人建议使用try/catch

getStateByCityName(cityName) {
    var states = {};
    try {
        states = JSON.parse(sessionStorage.getitem('states'));
    } catch (e) {
    }
    var states_keys = Object.keys(states);

    for (var i = 0, l = states_keys.length; i < l; i++) {
        if (states[states_keys[i]].indexOf(cityName) !== -1) {
            return states_keys[i];
        }
    }
    return false;
}

Answer 4

这应该有效，但无法测试：

function (arrayTarget, itemToSearch){
    for (x in arrayTarget) {
        for(y in arrayTarget[x])
            if(itemToSearch == arrayTarget[x][y])
                 return x;   
    }
}

Javascript数组迭代

4 个答案: