JS 从 http.get 分配 var

Question

trying to assign json data to global js variables... why does this not work... tried using fetch and this http.get keep getting undefined for the global vars when console.log displays them any help?

var https=require('https');
var testUrl="https://tools.learningcontainer.com/sample-json.json"
var firstName=""
var lastName=""
var age=0
function getNews(url1) {
var request = https.get(url1, function(response) {
    // console.log(response.statusCode); // for testing to see the status code
    var body = ''; // start with an empty body since node gets responses in chunks

    // Read the data
    response.on('data', function(chunk) {
    body += chunk;
             });
    
    response.on('end', function() {
    if ( response.statusCode === 200 ) {
       data=JSON.parse(body)
       //console.log(data)
        }
       assignData(data)  
    })
})
}

function assignData(data) { // function to process data
firstName=data.firstName
lastName=data.lastName
age=data.age
console.log(firstName,lastName,age)
}
    
getNews(testUrl);
console.log(firstName,lastName,age)

Answer 1

You have to wait until all data has been received and processed.

You can use for example "await / async"...

For demonstration purposes, I set a simple timeout at the end.

    var https = require('https');
    var testUrl = "https://tools.learningcontainer.com/sample-json.json"
    var firstName = ""
    var lastName = ""
    var age = 0
    function getNews(url1) {
        var request = https.get(url1, function (response) {
            // console.log(response.statusCode); // for testing to see the status code
            var body = ''; // start with an empty body since node gets responses in chunks
    
            // Read the data
            response.on('data', function (chunk) {
                body += chunk;
            });
    
            response.on('end', function () {
                if (response.statusCode === 200) {
                    data = JSON.parse(body)
                    //console.log('[response]',data)
                }
                assignData(data)
            })
        })
    }
    
    function assignData(data) { // function to process data
        firstName = data.firstName
        lastName = data.lastName
        age = data.age
        console.log('[assignData]', firstName, lastName, age)
    }
    
    getNews(testUrl);
    
console.log('[resultToEarly]', firstName, lastName, age)

setTimeout(function() {
    console.log('[resultAfterWaiting]', firstName, lastName, age)
    }, 3000);

Answer 2

https.get is an asynchronous function, to make it some code execute after it is completed you have to resort to the old good callback. Now, since you have it executed inside another function, to execute some code after that function is done with the request, you would have to wrap the http.get call in an Promise and await for it to finish , then execute whatever code you want after the getNews() call in an IIFE.

Take a look:

var testUrl = "https://tools.learningcontainer.com/sample-json.json"
var firstName = ""
var lastName = ""
var age = 0
function getNews(url1) {
    return new Promise(
        (resolve, reject) => {
            https.get(url1, function (response) {
                // console.log(response.statusCode); // for testing to see the status code
                var body = ''; // start with an empty body since node gets responses in chunks
        
        
                // Read the data
                response.on('data', function (chunk) {
                    body += chunk;
                });
        
                response.on('end', function () {
                    if (response.statusCode === 200) {
                        data = JSON.parse(body);
                        //    console.log(data)
                        assignData(data);
                    }
                    resolve();
                });

                response.on('error', function () {
                    reject(error);
                })
            })
        }
    )
}

function assignData(data) { // function to process data
    firstName = data.firstName
    lastName = data.lastName
    age = data.age
    // console.log(firstName,lastName,age)
}

(async function(){
    await getNews(testUrl);
    console.log(firstName, lastName, age)
})();