What is the work of callback argument in NodeJs "module.exports"?

[MaxySpark]

I’m learning nodeJS. I don’t know what is the purpose of

callback

argument in

module.exports

. It pretty much look like

return

and

console.log

here is my code

var request = require('request');

module.exports = function(location,callback) {

var encodedUrl = encodeURIComponent(location);
//set url
var url = "http://api.openweathermap.org/data/2.5/weather?q="+encodedUrl+"&APPID=575991c6b55a139d32139652d78bc8b8&units=metric";

//location check
if(!location) {
callback("No location provided");
} else {
callback('location is '+location);
}

//request
request({
url: url,
json: true
}, function (error,response, body) {
if(error) {
callback('Unable To Fetch Weather');
} else {
//console.log(JSON.stringify(body, null, 4));
callback("Current Temperature in "+body.name+" "+body.main.temp + '\xB0!!!');
}
});
};

[rah_sin]

The purpose of callback is to invoke appropriate callback method based on error and success condition after calling third party api.

rahul