How to sort HTML tables in JavaScript

A short while ago I blogged that KwaMoja now has the facility to sort HTML tables in JavaScript. I have had numerous requests to explain more about how this is done, so here is a brief tutorial on achieving this.

The table has to be constructed in a specific way. The area of the table to be sorted has to contain one row of <th> cells followed by any number of <td> rows.

So the following HTML would be suitable:

<tr>
        <th>Header1</th>
        <th>Header2</th>
</tr>
<tr>
        <td>Data11</td>
        <td>Data12</td>
</tr>
<tr>
        <td>Data21</td>
        <td>Data22</td>
</tr>

which will look like this:

Header1	Header2
Data11	Data12
Data21	Data22

This area to be sorted must be completely contained within a pair of tags, for instance between a <table> and a </table>. If you require other things in the table, then I generally use a <tbody> and a </tbody> to surround the area to be sorted.

The JavaScript function starts with the following:



1 function SortSelect(selElem) {
2    table=selElem.parentNode.parentNode;
3    headerRow = table.rows[0];

The function is called by clicking on the <th></th> element of the column that we wish to sort by. Thus the parameter "selElem" will be that cell. The parent of that cell will be the row (<tr>) containing the header, and the parent of the row will be the element that contains the whole of the sortable table.

Thus line 2 will give us the entire table that we wish to sort. Line 3 assigns the first row of that table to the variable "headerRow"

4    columnText=selElem.innerHTML;
5    for (var j = 0, col; col = headerRow.cells[j]; j++) {
6        if (headerRow.cells[j].innerHTML==columnText) {
7            columnNumber=j;
8    }

This section finds the column number that is to be sorted on. Line 4 finds the column header, and then lines 5 to 8 loop through the columns until the correct one is found.

09    var tmpArray = new Array();
10    for (var i = 1, row; row = table.rows[i]; i++) {
11        var rowArray = new Array();
12        for (var j = 0, col; col = row.cells[j]; j++) {
13            if (row.cells[j].tagName == 'TD' ) {
14                rowArray[j]=row.cells[j].innerHTML;
15            }
16        }
17        tmpArray[i]=rowArray;
18    }
 
This section gets the information from each cell, and feeds it into a JavaScript array object before sorting it. Line 9 creates the array object then we cycle through each row (starting at the second line, as the first contains the headings), creating an array object for each row, and finally line 17 adds that row array to the main array.

19    tmpArray.sort(
20        function(a,b) {
21                if (columnClass=="number") {
22                    return parseFloat(a[columnNumber])-parseFloat(b[columnNumber]);
23                } else if (columnClass=="date") {
24                    da=new Date(a[columnNumber]);
25                    db=new Date(b[columnNumber]);
26                    return da>db;
27                } else {
28                    return a[columnNumber].localeCompare(b[columnNumber])
29                }
30        }
31    );
 
This section performs a standard JavaScript 3d array sorting routine. It will sort by number, alphabetic, and date. Other sorting routines can be included as needed.

Finally we need to feed the sorted array back into the html table as here

32    for (var i = 0, row; row = table.rows[i+1]; i++) {
33        var rowArray = new Array();
34        rowArray=tmpArray[i];
35        for (var j = 0, col; col = row.cells[j]; j++) {
36            if (row.cells[j].tagName == 'TD' ) {
37                row.cells[j].innerHTML=rowArray[j];
38            }
39        }
40    } 
and we have fully sorted the HTML table in 40 lines of JavaScript. I have added in some nice formatting, and cursors in, and get the following full function:

function SortSelect(selElem) {
    var tmpArray = new Array();
    th=document.getElementById("Theme").value;
    columnText=selElem.innerHTML;
    table=selElem.parentNode.parentNode;
    row = table.rows[0];
    for (var j = 0, col; col = row.cells[j]; j++) {
        if (row.cells[j].innerHTML==columnText) {
            columnNumber=j;
            s=getComputedStyle(row.cells[j], null);
            if (s.cursor=="s-resize") {
                row.cells[j].style.cursor="n-resize";
                row.cells[j].style.backgroundImage="url('css/"+th+"/images/descending.png')";
                row.cells[j].style.backgroundPosition="right center";
                row.cells[j].style.backgroundRepeat="no-repeat";
                row.cells[j].style.backgroundSize="12px";
                direction="a";
            } else {
                row.cells[j].style.cursor="s-resize";
                row.cells[j].style.backgroundImage="url('css/"+th+"/images/ascending.png')";
                row.cells[j].style.backgroundPosition="right center";
                row.cells[j].style.backgroundRepeat="no-repeat";
                row.cells[j].style.backgroundSize="12px";
                direction="d";
            }
        }
    }
    for (var i = 1, row; row = table.rows[i]; i++) {
        var rowArray = new Array();
        for (var j = 0, col; col = row.cells[j]; j++) {
            if (row.cells[j].tagName == 'TD' ) {
                rowArray[j]=row.cells[j].innerHTML;
                columnClass=row.cells[columnNumber].className;
            }
        }
        tmpArray[i]=rowArray;
    }
    tmpArray.sort(
        function(a,b) {
            if (direction=="a") {
                if (columnClass=="number") {
                    return parseFloat(a[columnNumber])-parseFloat(b[columnNumber]);
                } else if (columnClass=="date") {
                    da=new Date(a[columnNumber]);
                    db=new Date(b[columnNumber]);
                    return da>db;
                } else {
                    return a[columnNumber].localeCompare(b[columnNumber])
                }
            } else {
                if (columnClass=="number") {
                    return parseFloat(b[columnNumber])-parseFloat(a[columnNumber]);
                } else if (columnClass=="date") {
                    da=new Date(a[columnNumber]);
                    db=new Date(b[columnNumber]);
                    return da<=db;
                } else {
                    return b[columnNumber].localeCompare(a[columnNumber])
                }
            }
        }
    );
    for (var i = 0, row; row = table.rows[i+1]; i++) {
        var rowArray = new Array();
        rowArray=tmpArray[i];
        for (var j = 0, col; col = row.cells[j]; j++) {
            if (row.cells[j].tagName == 'TD' ) {
                row.cells[j].innerHTML=rowArray[j];
            }
        }
    }
    return;
}

This is called by including this inline onclick handler

 onclick="SortSelect(this)"

I hope this explanation is useful to some people.