NodeJs: Collecting data across multiple “data” events using http.get()

Question

I have to collect multiple "data" events using http.get() and append them to a string and print it to the console. The last two console.log() statements always print 0 and an empty string. But the console.log() inside the http.get() prints all the received data correctly. The string str is a global variable so no scope problems. Then why does the last line print an empty string?

// JavaScript File
var http = require('http');

var str = '';

http.get(process.argv[2], function(response){
    response.on('error', console.error);
    response.on('data', function(data){
       str += data.toString();
    });
    response.on('end', function(){
        console.log(str); //works fine, prints the received data
    );
}).on('error', console.error);

console.log(str.length); // prints 0
console.log(str); // prints empty string

Answer 1

This is a common gotcha when working with node. You are dealing with an asynchronous request when you use http.get() . What this means is you final console.log() statement will be called before the callback functions within http.get().

With your code the order of events goes something like this:

• define str
• initiate http.get()
• final two console.log() statements
• receive data from http.get()
• add to str
• console.log() inside the http.get() callbacks

So everything is working, you are just asking for the data before you have received it.