Javascript prototype override

Question

I have this code that allows me to return a string about the posts connected to a particular post. I tried to use the bracket and dot notation in accessing properties below in the list part (list=list+this["connectionsTo"[i]].postNum+"\n";) but doesn't work. But then when I used the double dot notation, it worked, why? I believe those two are the same.

function Fencepost(x, y, postNum) {
  this.x = x;
  this.y = y;
  this.postNum = postNum;
  this.connectionsTo = [];
}

Fencepost.prototype = {
  sendRopeTo: function(connectedPost) {
    this.connectionsTo.push(connectedPost);
  },
  removeRope: function(removeTo) {
    var temp = [];
    for (var i = 0; i < this.connectionsTo.length; i++) {
      if (this.connectionsTo[i].postNum != removeTo) {
        temp.push(this.connectionsTo[i]);
      }
    }
    this.connectionsTo = temp;
  },
  movePost: function(x, y) {
    this.x = x;
    this.y = y;
  },
  valueOf: function() {
  return Math.sqrt(this.x * this.x +
                   this.y * this.y);
  }
};

Fencepost.prototype.toString=function(){
var list="";
for(var i=0;i<this.connectionsTo.length;i++){
list=list+this["connectionsTo"[i]].postNum+"\n";
}
  return "Fence post #"+this.postNum+":\nConnected to posts:\n"+list+"Distance from ranch: "+this.valueOf()+" yards";
};

var post10=new Fencepost(3,4,10);
var post11=new Fencepost(5,7,11);
var post12=new Fencepost(6,7,12);
var post13=new Fencepost(8,9,13);
post10.sendRopeTo(post11);
post10.sendRopeTo(post12);
post10.sendRopeTo(post13);
console.log(post10.toString());

"doesn't work". Ok. What error did you get? Check the javascript console when you try to execute this code and report back what you find. — Joseph Marikle, Apr 26 '17 at 13:13
"anything"[n] isn't going to work the way you expect. Not sure what double dot notation is. — Dave Newton, Apr 26 '17 at 13:15
Hi mister I'm new to JS (started 10 days ago) and this is what I find in JS Bin:"error" "TypeError: Cannot read property 'postNum' of undefined at Fencepost.toString (hezecawilo.js:38:35) at hezecawilo.js:50:45 at https://static.jsbin.com/js/prod/runner-3.41.10.min.js:1:13926 at https://static.jsbin.com/js/prod/runner-3.41.10.min.js:1:10855" — , Apr 26 '17 at 13:15
`"connectedTo"[i]` evaluates to the i-th character of "connectedTo" — le_m, Apr 26 '17 at 13:15
ya mister I edited the question, that was supposed to be ["connectionsTo"[i]].postNum, still doesnt work — , Apr 26 '17 at 13:16
`"connectionsTo"[i]` will return a character at the i position. I believe you wanted `this["connectionsTo"][i]` — bzim, Apr 26 '17 at 13:18
`property 'postNum'` is missing because `this[c] .. this[o] .. this[n]` are all undefined. You're trying to get `this["connectionsTo"][i]`, but as Bergi pointed out, you're getting the individual characters of the string `connectionsTo` instead. — Joseph Marikle, Apr 26 '17 at 13:19
The logic of *removeRope* is broken. It assigns a new array to *this.connectionsTo*, but any existing reference to that property will continue to reference the old (unmodified) array. You should *splice* the match from *connectionsTo*, not create and assign a new array from the non-matches (which is illogical, inefficient and likely the source of future obscure bugs). — RobG, Apr 26 '17 at 13:25

score 4 · Accepted Answer · answered Apr 26 '17 at 13:15

4

Since you are iterating over the this.connectionsTo array, you are looking for

this["connectionsTo"][i]

or the equivalent

this.connectionsTo[i]

instead of

this["connectionsTo"[i]]

which indexes the string, and then takes that character for the property of this.

answered Apr 26 '17 at 13:15

Bergi

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@MarkLemuelGenita The edit concerns `"connectedTo"` vs `"connectionsTo"`, which is not what I am talking about – Bergi Apr 26 '17 at 13:19
a follow-up question mister, why sometimes JS Bin requires me to use bracket and dot notation (accessing a property of an object within an object) and sometimes it doesn't? – Apr 26 '17 at 13:26
See [the question](https://stackoverflow.com/questions/4968406/javascript-property-access-dot-notation-vs-brackets) I had linked in my answer. You can always use bracket notation, but for constant identifier-named properties dot notation is easier to read. – Bergi Apr 26 '17 at 13:28

Javascript prototype override

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