Node.js: javascript PLO, why such designs?

[Raziyah00]

Started studying Node.js and often sees such designs:

var Network = function(url) {
    this.url = url;
}

Why are they taking their current properties inside?

[Amritpal]

Network is probably a design function (generally class). A copy of the class will be created later. If the url is available to all methods of the new facility, the variable url must be recorded in the object ' s properties. Try the next code and see what it is.

Network = function(url) { this.url = url; }
Network.prototype = {
    testProperties: function() {
      console.log(typeof url); // undefined;
      console.log(this.url); // ru.stackoverflow.com
    }
};
var stackoverflow = new Network('ru.stackoverflow.com');
stackoverflow.testProperties();