Using jQuery to change image map coord values

Question

I have a pretty complex image map that I would like to shrink by half. To do so would require dividing all the coord values by 2. Since there are thousands of coord values, I was thinking that I could use jQuery to traverse the DOM to find the coord values, and divide them by two. I'm pretty amateur when it comes to JavaScript and jQuery and I wrote the following code that doesn't work to accomplish my task:

$(function(){
    $('area').each(function(){
        coord_vals= $('area'[coords]).split(',');
        new_vals= coord_vals/2;
        $('area'[coords]).val(new_vals + ',');
    });
});

Here's the first few lines of HTML I'm trying to traverse:

<div id="map">
    <img class="map" src="images/us_map.jpg" width="960" height="593" usemap="#usa">
    <map name="usa">
    <area href="#" title="SC" shape="poly" coords="735,418, 734,419, 731,418, 731,416, 729,413, 727,411, 725,410, 723,405, 720,399, 716,398, 714,396, 713,393, 711,391, 709,390, 707,387, 704,385, 699,383, 699,382, 697,379, 696,378, 693,373, 690,373, 686,371, 684,369, 684,368, 685,366, 687,365, 687,363, 693,360, 701,356, 708,355, 724,355, 727,356, 728,360, 732,359, 745,358, 747,358, 760,366, 769,374, 764,379, 762,385, 761,391, 759,392, 758,394, 756,395, 754,398, 751,401, 749,404, 748,405, 744,408, 741,409, 742,412, 737,417, 735,418"></area>
    <area href="#" title="HI" shape="poly" coords="225,521, 227,518, 229,517, 229,518, 227,521, 225,521"></area>
    <area href="#" title="HI" shape="poly" coords="235,518, 241,520, 243,520, 244,516, 244,513, 240,512, 236,514, 235,518"></area>

Answer 1

You were on the right track it's just you didn't use $(this) in your loop. Also, to get the coords, you can use attr('coords')

Fixed version

$(function(){ 
   $('area').each(function(){
      var coord_vals = $(this).attr('coords').split(',');
      var new_vals;
      for(var i=0; i<coord_vals.length; i++) {
          new_vals[i] = coord_vals[i] / 2;
      }
      new_vals = new_vals.join(",");
      $(this).attr('coords').val(new_vals);
   });
});

Answer 2

You can do it like this:

$("area").each(function() {
    var pairs = $(this).attr("coords").split(', ');
    for(var i=0; i<pairs.length; i++) {
        var nums = pairs[i].split(',');
        for(var j=0; j<nums.length; j++) {
            nums[j] = parseFloat(nums[j]) /2;
        }
        pairs[i] = nums.join(',');
    }
    $(this).attr("coords", pairs.join(', '));
});

This maintains the formats and converts each valid carefully, here's the output:

<div id="map">
  <img class="map" src="images/us_map.jpg" width="960" height="593" usemap="#usa"> 
  <map name="usa"> 
    <area href="#" title="SC" shape="poly" coords="367.5,209, 367,209.5, 365.5,209, 365.5,208, 364.5,206.5, 363.5,205.5, 362.5,205, 361.5,202.5, 360,199.5, 358,199, 357,198, 356.5,196.5, 355.5,195.5, 354.5,195, 353.5,193.5, 352,192.5, 349.5,191.5, 349.5,191, 348.5,189.5, 348,189, 346.5,186.5, 345,186.5, 343,185.5, 342,184.5, 342,184, 342.5,183, 343.5,182.5, 343.5,181.5, 346.5,180, 350.5,178, 354,177.5, 362,177.5, 363.5,178, 364,180, 366,179.5, 372.5,179, 373.5,179, 380,183, 384.5,187, 382,189.5, 381,192.5, 380.5,195.5, 379.5,196, 379,197, 378,197.5, 377,199, 375.5,200.5, 374.5,202, 374,202.5, 372,204, 370.5,204.5, 371,206, 368.5,208.5, 367.5,209">
    <area href="#" title="HI" shape="poly" coords="112.5,260.5, 113.5,259, 114.5,258.5, 114.5,259, 113.5,260.5, 112.5,260.5">
    <area href="#" title="HI" shape="poly" coords="117.5,259, 120.5,260, 121.5,260, 122,258, 122,256.5, 120,256, 118,257, 117.5,259"> 
  </map>
</div>

You can give it a try here.

Answer 3

I think it might be best to write some code to produce a new code for you. Doing this will reduce the initialization time and make your users happier. I threw together a demo, basically it fills a textarea with the transformed code with which you just replace the original.

HTML

<div id="map">
 <img class="map" src="images/us_map.jpg" width="960" height="593" usemap="#usa">
 <map name="usa">
  <area href="#" title="SC" shape="poly" coords="735,418, 734,419, 731,418, 731,416, 729,413, 727,411, 725,410, 723,405, 720,399, 716,398, 714,396, 713,393, 711,391, 709,390, 707,387, 704,385, 699,383, 699,382, 697,379, 696,378, 693,373, 690,373, 686,371, 684,369, 684,368, 685,366, 687,365, 687,363, 693,360, 701,356, 708,355, 724,355, 727,356, 728,360, 732,359, 745,358, 747,358, 760,366, 769,374, 764,379, 762,385, 761,391, 759,392, 758,394, 756,395, 754,398, 751,401, 749,404, 748,405, 744,408, 741,409, 742,412, 737,417, 735,418"></area>
  <area href="#" title="HI" shape="poly" coords="225,521, 227,518, 229,517, 229,518, 227,521, 225,521"></area>
  <area href="#" title="HI" shape="poly" coords="235,518, 241,520, 243,520, 244,516, 244,513, 240,512, 236,514, 235,518"></area>
 <!-- ETC -->
 </map>
</div>

<textarea id="newAreaTags"></textarea>

Script

$(document).ready(function(){
 var newmap = '', coords;
 $('map[name=usa]').find('area').each(function(){
  newmap += '<area href="#" title="' + $(this).attr('title') +
   '" shape="' + $(this).attr('shape') + '" coords="';
  coords = $(this).attr('coords').replace(/\s+/g,'').split(',');
  for (var i = 0; i < coords.length; i++){
   coords[i] = Math.round(parseInt( coords[i], 10) / 2);
  }
  newmap += coords.join(',') + '"></area>\n';
 });
 $('#newAreaTags').val(newmap);
})