NodeJS-主文件未收到函数内部的lookupService返回

Question

So I have a file called 'myinternet_utils.js' and the following function:

 exports.hasInternet = function () { require('dns').lookupService('8.8.8.8', 53, function (err, hostname, service) { return hostname; }); }; 

I also have a file called 'server.js', where I have this piece of code:

 var ieUtils_ = require('./myinternet_utils.js'); console.log( ieUtils_.hasInternet() ); 

The 'console.log' prints 'undefined'.

Why am I not getting the output of the function hasInternet?

Answer 1

It seems like the function you are using is asynchronous. Also your function does not actually return anything, so even if it was synchronous you would still get undefined . Try this instead, using promises:

exports.hasInternet = function () {

    return new Promise(function(resolve, reject) {
        require('dns').lookupService('8.8.8.8', 53, function (err, hostname, service) {
            if(err){
                return reject(err);
            }
            resolve(hostname);
        });
    });

};

and in the main file

var ieUtils_ = require('./myinternet_utils.js');

ieUtils_.hasInternet().then(function(result){
    console.log(result);
})