如何使用JavaScript從JSON數組獲取JSON值

Question

我正在使用javascript從json數組獲取值。我是json數組的初學者，但我不知道如何執行此操作。我的json數組如下所示：

{
  "disclaimer": "Exchange rates are provided for informational purposes only, and do not constitute financial advice of any kind. Although every attempt is made to ensure quality, NO guarantees are given whatsoever of accuracy, validity, availability, or fitness for any purpose - please use at your own risk. All usage is subject to your acceptance of the Terms and Conditions of Service, available at: https://openexchangerates.org/terms/",
  "license": "Data sourced from various providers with public-facing APIs; copyright may apply; resale is prohibited; no warranties given of any kind. Bitcoin data provided by http://coindesk.com. All usage is subject to your acceptance of the License Agreement available at: https://openexchangerates.org/license/",
  "timestamp": 1416297649,
  "base": "USD",
  "rates": {
    "AED": 3.673191,
    "AFN": 58.008151,
    "ALL": 112.1323,
    "AMD": 415.972002,
    "ANG": 1.78696,
    "AOA": 100.644875,
    "ARS": 8.508199,
    "AUD": 1.145932,
    "AWG": 1.79,
    "AZN": 0.7843,
    "BAM": 1.567493,
    "BBD": 2,
    "BDT": 77.32636,
    "BGN": 1.567435,
    "BHD": 0.376895,
    "BIF": 1556.029233,
    "BMD": 1,
    "BND": 1.298167,
    "BOB": 6.908841,
    "BRL": 2.607403,
    "BSD": 1,
    "BTC": 0.0025684709,
    "BTN": 61.7715,
    "BWP": 9.257686,
    "BYR": 10814.633333,
    "BZD": 1.997764,
    "CAD": 1.127204,
    "CDF": 925.406333,
    "CHF": 0.962128,
    "CLF": 0.02436,
    "CLP": 595.853895,
    "CNY": 6.12456,
    "COP": 2154.505,
    "CRC": 538.195095,
    "CUP": 1.000738,
    "CVE": 87.892625,
    "CZK": 22.17167,
    "DJF": 178.03412,
    "DKK": 5.961459,
    "DOP": 43.68968,
    "DZD": 84.73913,
    "EEK": 12.5279,
    "EGP": 7.147473,
    "ERN": 15.062575,
    "ETB": 20.09255,
    "EUR": 0.801147,
    "FJD": 1.934408,
    "FKP": 0.638658,
    "GBP": 0.638658,
    "GEL": 1.76438,
    "GGP": 0.638658,
    "GHS": 3.21655,
    "GIP": 0.638658,
    "GMD": 43.08885,
    "GNF": 7084.038333,
    "GTQ": 7.612101,
    "GYD": 206.740124,
    "HKD": 7.754716,
    "HNL": 21.22432,
    "HRK": 6.145546,
    "HTG": 46.35835,
    "HUF": 245.287701,
    "IDR": 12156.366667,
    "ILS": 3.836499,
    "IMP": 0.638658,
    "INR": 61.74318,
    "IQD": 1176.692567,
    "IRR": 26711.333333,
    "ISK": 123.965999,
    "JEP": 0.638658,
    "JMD": 112.8815,
    "JOD": 0.706622,
    "JPY": 116.5573,
    "KES": 90.07741,
    "KGS": 57.6,
    "KHR": 4059.736567,
    "KMF": 394.713449,
    "KPW": 900,
    "KRW": 1098.851659,
    "KWD": 0.291222,
    "KYD": 0.82625,
    "KZT": 180.936999,
    "LAK": 8049.581667,
    "LBP": 1511.646667,
    "LKR": 130.990299,
    "LRD": 91.50915,
    "LSL": 11.11745,
    "LTL": 2.765696,
    "LVL": 0.562739,
    "LYD": 1.206794,
    "MAD": 8.838571,
    "MDL": 15.071,
    "MGA": 2720.776667,
    "MKD": 49.38793,
    "MMK": 1030.461733,
    "MNT": 1874.666667,
    "MOP": 7.986375,
    "MRO": 290.8235,
    "MTL": 0.683738,
    "MUR": 31.6021,
    "MVR": 15.28127,
    "MWK": 457.6505,
    "MXN": 13.57063,
    "MYR": 3.352459,
    "MZN": 31.100225,
    "NAD": 11.11885,
    "NGN": 172.279401,
    "NIO": 26.61524,
    "NOK": 6.766937,
    "NPR": 99.04372,
    "NZD": 1.258938,
    "OMR": 0.38502,
    "PAB": 1,
    "PEN": 2.931746,
    "PGK": 2.560203,
    "PHP": 44.94794,
    "PKR": 101.784399,
    "PLN": 3.380801,
    "PYG": 4666.459993,
    "QAR": 3.640328,
    "RON": 3.551761,
    "RSD": 96.324459,
    "RUB": 47.07185,
    "RWF": 691.6032,
    "SAR": 3.752252,
    "SBD": 7.443016,
    "SCR": 14.17481,
    "SDG": 5.686665,
    "SEK": 7.409777,
    "SGD": 1.297628,
    "SHP": 0.638658,
    "SLL": 4361.666667,
    "SOS": 786.04194,
    "SRD": 3.275,
    "STD": 19621.866667,
    "SVC": 8.750655,
    "SYP": 168.829401,
    "SZL": 11.11241,
    "THB": 32.79493,
    "TJS": 5.080025,
    "TMT": 2.85,
    "TND": 1.833351,
    "TOP": 1.984081,
    "TRY": 2.228282,
    "TTD": 6.34007,
    "TWD": 30.72224,
    "TZS": 1723.825,
    "UAH": 15.49353,
    "UGX": 2731.136667,
    "USD": 1,
    "UYU": 24.17477,
    "UZS": 2405.860013,
    "VEF": 6.30235,
    "VND": 21329.55,
    "VUV": 98.452501,
    "WST": 2.385222,
    "XAF": 526.037765,
    "XAG": 0.06207936,
    "XAU": 0.00083957,
    "XCD": 2.70156,
    "XDR": 0.682345,
    "XOF": 526.128025,
    "XPF": 95.673269,
    "YER": 214.9703,
    "ZAR": 11.09921,
    "ZMK": 5253.075255,
    "ZMW": 6.373054,
    "ZWL": 322.355006
  }
}

我的JavaScript函數是這樣的：

  function GetBalanceQty(val) {
            //in val u get dropdown list selected value
            var id = val;
            alert("value=" + id);


            var xmlhttp = new XMLHttpRequest();
            var url = "https://openexchangerates.org/api/latest.json?app_id=324d066072324a7fba34618f5c5dfd83";

            xmlhttp.onreadystatechange = function () {
                if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
                    myFunction(xmlhttp.responseText);
                }
            }
            xmlhttp.open("GET", url, true);
            xmlhttp.send();

            function myFunction(response) {
                var arr = JSON.parse(response);


 // Logic to display value of currency (contained in val argument) in jason array.


            }

我的javascript函數GetBalanceQty（val）現在在val參數中接收3個字母的貨幣名稱，我想顯示其對應的值。

Answer 1

function myFunction(response) {
    var currencyData = JSON.parse(response);

    if (!currencyData.rates) {
        // possibly handle error condition with unrecognized JSON response
        alert("currency data not found!");
    }

    // id variable is available from outer function
    if (id in currencyData.rates) {
        alert(currencyData.rates[id]);
    } else {
        alert("unknown currency code!");
    }
}