For loop skipping over the rest of items in an array after two iterations

Question

Apology:

I apologize if this is a really basic question, I've looked around but since I never did get a very solid grounding in Javascript objects, I may be looking for answers in all the wrong places. That, and I don't have a solid enough grasp of Javascript to seperate out what is Javascript in all of the JQuery questions, and I don't want to use JQuery until I have a better understanding of Javascript in general. Thank you.

Problem:

I have a for loop that is going through an array of Google Map markers, to return them to active on the map I have open. The markers still exist somehow in the array because they return randomly when I iterate a couple times through this block of code. It will make it through one or two iterations of the loop, and then end. I added the hasOwnProperty test once I noticed the error, but this isn't skipping past the problem item in the array like I thought it should.

Question:

Why is my for loop skipping over objects in the array that I know are there?

//Code Loop
for (var i in removedMarkerArray)
{
  //test for valid object
  if (!removedMarkerArray[i].hasOwnProperty('title')) continue;
  else alert("You dawg, this stuff passed.");

  //the actual code doing real work, rather than testing.
  if (removedMarkerArray[i].PD == PD)
  {
    removedMarkerArray[i].setMap(map);

    placedMarkerArray.push(removedMarkerArray[i]);
    removedMarkerArray.splice(i, 1);
  }
}

//Example object in the array.
var marker = new google.maps.Marker({
    map: map,
    position: results[0].geometry.location,
    title: location.mouseover,
    PD: location.PD
});

Thank you for reading through my question, and I'm looking forward to any answers.

Please shorten the question and refactor it so there will be a boring, non-related part where you write whatever you want, and then a part containing the real question, so I could focus on that. — vsync
– vsync, Commented Nov 10, 2015 at 20:00
I've cleaned up the Question section, and broke out a Problem section. Is that explaining the problem that I'd like answered better? — Matthew_Sp
– Matthew_Sp, Commented Nov 10, 2015 at 20:29
you should change your for in loop to a classic for loop as I indicated in my answer below as well as put a console.log(removedMarkerArray[i]) as the first line in your for loop to see what that output is and if you are hitting each expected marker. — Abdullah Rasheed
– Abdullah Rasheed, Commented Nov 10, 2015 at 20:39
I've added the "" console.log(removedMarkerArray[i]) "" to the first line within the for loop. I can clearly see the objects coming through, but only one or two make it to the actual map, rather than all of them. I kept the alert in place, and it's still only coming up twice when I run this code. I don't see any objects I didn't expect in there. — Matthew_Sp
– Matthew_Sp, Commented Nov 10, 2015 at 20:45
in the console, when you collapse all of your objects, do they have the PD property? the next thing I would do is check to make sure all of those objects are actually hitting the line: removedMarkerarray[i].setMap(map); — Abdullah Rasheed
– Abdullah Rasheed, Commented Nov 10, 2015 at 20:52

Community · Accepted Answer · 2017-05-23 12:23:39Z

3

for...in is meant to iterate over the Properties of an Object. Use a regular for loop if its meant to iterate through the indicies of an array.

This answer explains why: https://stackoverflow.com/a/5263872/1385467

edited May 23, 2017 at 12:23

CommunityBot

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answered Nov 10, 2015 at 20:03

Adam Finley

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2 Comments

Matthew_Sp Over a year ago

I did change my code to use a normal for loop instead of the for...in loop. I understand that this is good practice, but it doesn't appear to have fixed my problem. Do you have any other advice?

Matthew_Sp Over a year ago

I found the actual answer. Thank you for helping me be a better Javascript programmer in the future, but your answer did not help me solve this problem at all.

Abdullah Rasheed · Accepted Answer · 2015-11-10 20:42:12Z

1

If removedMarkerArray is a true Array you should use a classic for loop rather than for in. So you should be doing something of the sort:

for(var i = 0, n = removedMarkerArray.length; i < n; i++){
    console.log(removedMarkerArray[i]); //check desired object in console for debugging
    ..code here
}

edited Nov 10, 2015 at 20:42

answered Nov 10, 2015 at 20:03

Abdullah Rasheed

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5 Comments

Matthew_Sp Over a year ago

I updated the question with an example of what I'm putting in the array. Just so I understand, it's an array and not an object? I declared the variable originally with "var removedMarkerArray = [];", and used push to add the objects to the array.

Abdullah Rasheed Over a year ago

Yes, its an array if you declared it with the Array literal syntax, var removedMarkerArray = [], but Array's are objects. If you want to iterate through the indices as Adam Pointed out you should use the classic for-loop that i posted, but if you want to iterate through the properties you would use for-in loop. I'll take a look at the updated question.

Abdullah Rasheed Over a year ago

@Matthew_Sp if you put console.log(removedMarkerArray[i]); in your for loop do you see the desired object each time?

Matthew_Sp Over a year ago

I commented on the original question, because that's where I saw you mention it, and you hadn't updated your question yet. I did add the logging to console command, and I'm getting all of the objects that disappear in another section of code, but not all of the objects are returning to the screen. I am pretty sure it's this chunk of code, because the alert I left in is only iterating twice.

Matthew_Sp Over a year ago

I found the answer, and I've added it as an answer here. Thank you for your help, it let me to the answer with a clear mind this morning.

pherris · Accepted Answer · 2015-11-10 20:54:53Z

0

I like forEach for better readability as long as you are using a real Array.

removedMarkerArray.forEach(function(removedMarker, index) {
  //test for valid object
  if (!removedMarker.hasOwnProperty('title')) continue;
  else console.log("You dawg, this stuff passed.");

  //the actual code doing real work, rather than testing.
  if (removedMarker.PD == PD)
  {
    removedMarker.setMap(map);

    removedMarkerArray.splice(index, 1);
    placedMarkerArray.push(removedMarker);
  }
});

edited Nov 10, 2015 at 20:54

answered Nov 10, 2015 at 20:12

pherris

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2 Comments

Matthew_Sp Over a year ago

I'm not sure I'm following you. From what I was digging up on Splice, it should be removing just the object I'm working on from the array. Just before that, I'm pushing the marker I'm about to delete to another array so I don't lose it. Is there something else going on in the background I'm not aware of?

pherris Over a year ago

I missed the different variable name - thinking you were replacing it in the removedMarkerArray. Updated answer.

Matthew_Sp · Accepted Answer · 2015-11-11 15:28:13Z

The problem with my code removing a marker from the map stems not from the fact that I used for...in instead of a true for loop, which the highest rated question stated, it stemmed from that I was skipping over items in my array. When I was originally writing this, I assumed for...in would protect me from that, but as far as this is concerned, it worked just like the loop below.

I added a decrement on the i variable, so that it would run through the same index again instead of skipping one. This is now touching on all of the markers in my arrays.

for (var i = 0; i < placedMarkerArray.length; i++)
{
  if (placedMarkerArray[i].PD === PD)
  {
    placedMarkerArray[i].setMap(null);

    console.log(placedMarkerArray[i]);

    removedMarkerArray.push(placedMarkerArray[i]);
    placedMarkerArray.splice(i, 1);
>>  i--;
  }
}

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