如何在Javascript中访问对象的属性

Question

I am working on a project and currently learning Javascript. Right now, I am wondering how I can create an object with a constructor, assign attributes to it, and later read and modify these attributes. I think I got the creation and the assigning part right, but I can't seem to access any of my object's attributes from the outside.

function initialize() { 
    var testPlane = jet("9C3476", currentAirport, "Palma De Mallorca", "02:45", "Departed");

    alert("Never get to this point: " + testPlane.id);
}


function jet(id, from, to, expected, status) {
    this.id = id;
    this.from = from;
    this.to = to;
    this.expected = expected;
    this.status = status;
    this.position = from;
    alert("Id: "+ id + " From:" + from + " To: " + to + " Expected: " + expected + " Status: " + status);
    this.marker = new google.maps.Marker({
      position : this.position,
      icon : img,
      map : map,
    });
}

Answer 1

Check your browser console:

TypeError: Cannot read property 'id' of undefined

Use new to treat jet as a constructor:

var testPlane = new jet("9C3476", currentAirport, "Palma De Mallorca", "02:45", "Departed");

Without new , the code assigns whatever value jet() returns to testPlane , but since jet does not return anything at all, testPlane is undefined .

Answer 2

If you want to use the function "jet" as constructor, you need to call it with "new" as -

var testPlane = new jet("9C3476", currentAirport, "Palma De Mallorca", "02:45", "Departed");

OR

put this line inside function "jet" -

if(!(this instanceof jet)) {
    return new jet("9C3476", currentAirport, "Palma De Mallorca", "02:45", "Departed");
}

Also.. i hope "currentAirport", "google" are defined in your code.