如何使用JavaScript从JSON数组获取JSON值

Question

I am using javascript to get value from json array.I am a beginner with the json array and I am not able to get idea how to do this.My json array is comes like this:

{
  "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
  }
}

My javascript function is like this:

  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.


            }

My javascript function GetBalanceQty(val) recieves 3 letter currency name in val argument now I want to display its corresponding value.

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!");
    }
}