jQuery find previous table row that has a cell with a specific class

Suppose I have a table like so:

<table>
    <tr><td class="this-is-a-label">Label Cell</td></tr>
    <tr><td>Detail 1</td></tr>
    <tr><td class="selected">Detail 2</td></tr>
</table>

I want to be able to grab the previous "Label Cell" from the "Selected" cell.

My jQuery script should be something like:

$('.selected').each(function() {
    var label = $(this).parent().prev('tr td.th开发者_运维技巧is-is-a-label');
    //... do what I need with the label ...
});

But it's not working.

Does anyone have any suggestions?

You can do this:

$('.selected').each(function() {
  var label = $(this).closest('tr').prevAll('tr:has(td.this-is-a-label):first')
                     .children('td.this-is-a-label');
  //... do what I need with the label ...
});

This isn't ideal though, it's a rather expensive DOM traversal, if you can guarantee it's always 2 rows behind, you can do this:

$(this).closest('tr').prev().prev().children('td.this-is-a-label')

...which is much faster, it just depends what assumptions and guarantees you can make about your markup, if there are any certainties, you can definitely make it faster.

How about:

var label = 
  $('.selected').parent().prevAll('tr').children('td.this-is-a-label')[0];

$("td.selected").parents("table").find("td.this-is-a-label").text();

Here's how you get references to both the <tr> and <td> dom elements:

$("tr:has(td.selected)").each(function(i, trSel){
    var trLabel = $(trSel).prevAll("tr:has(td.this-is-a-label)").get(0);

    var tdSel = $(trSel).children("td.selected").get(0);
    var tdLabel = $(trLabel).children("td.this-is-a-label").get(0);

    console.log(trSel, tdSel);
    console.log(trLabel, tdLabel);
});

I created a little plugin in response to this post for the purpose of finding a cell which is relative to the current cell:

$.fn.cellFromCell = function(r,c,upOrDown) {
    if(upOrDown == 'down') {
        return $(this).parent().prevAll(':eq(' + r + ')').find('td:eq(' + c + ')').text();
    } else {
        return $(this).parent().nextAll(':eq(' + r + ')').find('td:eq(' + c + ')').text();
    }
}

alert($('.selected').cellFromCell(1, 0, 'down')); // alerts "Label Cell"
alert($('.this-is-a-label').cellFromCell(0, 0)); // alerts "Detail 1"
​

I used your html for a simple test case. You can mess with it here: http://jsfiddle.net/6kfVL/3/ ​

You can make it easy by coding in an HTML5 id tag when generating the table:

<table id="myTable">
    <tr id="label1"><td class="this-is-a-label">Label Cell</td></tr>
    <tr data-parent-label-id="label1"><td>Detail 1</td></tr>
    <tr data-parent-label-id="label1"><td class="selected">Detail 2</td>   </tr>
</table>

You can then use the value, and even perform actions on the associated "parent":

$("#myTable").on("click", "tr", function() {
    var associatedLabelId = $(this).data("parent-label-id");
    alert("Parent label of the row clicked: " + associatedLabelId);
    $("#" + associatedLabelId).addClass("highlight");
}