Question

我正在尝试学习Node.js

我无法在函数上创建自己的回调。看起来这么简单，但我不太明白该怎么做。

该函数传递一个地址（例如：＆＃34; 1234将ln，co＆＃34;），它使用google的geolocate json api返回数组中的完整地址，纬度和经度。

这是我的代码：

//require secure http module
var https = require("https");

//My google API key
var googleApiKey = "my_private_api_key";

//error function
function printError(error) {
    console.error(error.message);
}

function locate(address) {
//accept an address as an argument to geolocate

    //replace spaces in the address string with + charectors to make string browser compatiable
    address = address.split(' ').join('+');

    //var geolocate is the url to get our json object from google's geolocate api
    var geolocate = "https://maps.googleapis.com/maps/api/geocode/json?key=";
    geolocate += googleApiKey + "&address=" + address;

    var reqeust = https.get(geolocate, function (response){

        //create empty variable to store response stream
        var responsestream = "";

        response.on('data', function (chunk){
            responsestream += chunk;
        }); //end response on data

        response.on('end', function (){
            if (response.statusCode === 200){
                try {
                    var location = JSON.parse(responsestream);
                    var fullLocation = {
                        "address" : location.results[0].formatted_address,
                        "cord" : location.results[0].geometry.location.lat + "," + location.results[0].geometry.location.lng
                    };
                    return fullLocation;
                } catch(error) {
                    printError(error);
                }
            } else {
                printError({ message: "There was an error with Google's Geolocate. Please contact system administrator"});
            }
        }); //end response on end

    }); //end https get request

} //end locate function

所以当我尝试执行我的功能时

var testing = locate("7678 old spec rd");
console.dir(testing);

控制台记录未定义，因为它没有等待从locate返回（或者至少我猜这是问题所在）。

如何创建回调，以便当locate函数返回我的数组时，它会在它返回的数组上运行console.dir。

谢谢！我希望我的问题有道理，我自学成才，所以我的技术术语太可怕了。

Answer 1

您需要将回调函数传递给您的方法 - 因此回调可能看起来像这样

function logResult(fullLocation){
    console.log(fullLocation)
}

您可以将此传递到您的locate方法以及输入：

// note: no parentheses, you're passing a reference to the method itself, 
// not executing the method
locate("1234 will ln, co",logResult)

您也可以内联执行此操作 - 非常类似于您已经处理过的response对象：

locate("1234 will ln, co",function(fullLocation){
    // do something useful here
})

现在对于你方法中的位，而不是尝试return结果，你只需用结果调用回调：

function locate(address, callback) {
    ......

    response.on('end', function (){
        if (response.statusCode === 200){
            try {
                var location = JSON.parse(responsestream);
                var fullLocation = {
                    "address" : location.results[0].formatted_address,
                    "cord" : location.results[0].geometry.location.lat + "," + location.results[0].geometry.location.lng
                };
                callback(fullLocation); // <-- here!!!
            } catch(error) {
                printError(error);
            }
        } else {
            printError({ message: "There was an error with Google's Geolocate. Please contact system administrator"});
        }
    }); //end response on end

    .....
}

创建回调以从函数返回数组

1 个答案: