jsFiddle demo - Table Sort (vanilla JS)

fiddle.css

table {
	border: solid 1px #fc0;
	border-collapse: collapse;
}

table caption {
	font-weight: bold;
	font-size: 125%;
	text-transform: uppercase;
}

.footnote {
	font-size: 75%;
	color: #666;
}

table caption,
table th,
table td,
.footnote {
	font-family: Arial, Helvetica, sans-serif;
	padding: .5em;
}

table td {
	border: solid 1px #c96;
}


table th {
	background-color: #ec9;
	color: #630;
	border-bottom: solid 1px #c96;
}

table thead th {
	background: #fea;
	border-bottom: solid 3px #630;
}

table thead th a {
	color: #630;
	display: block;
	padding: 0 17px;
	background: #fea url(http://wps.scopevale.net/scripts/css/tablesort/arrow-up.gif) no-repeat right center;
}

table thead th.asc a {
	background: #fea url(http://wps.scopevale.net/scripts/css/tablesort/arrow-up-sel.gif) no-repeat right center;
}

table thead th.dsc a {
	background: #fea url(http://wps.scopevale.net/scripts/css/tablesort/arrow-dn-sel.gif) no-repeat right center;
}

fiddle.html

        <table id="sales" summary="Quarterly Sales (stated in millions of dollars)">
            <caption>Quarterly Sales*</caption>
            <thead>
                <tr>
                    <th>Companies</th>
                    <th>Q1</th>
                    <th>Q2</th>
                    <th>Q3</th>
                    <th>Q4</th>
                </tr>
            </thead>
            <tbody>
                <tr>
                    <th>Company A</th>
                    <td>$621</td>
                    <td>$942</td>
                    <td>$224</td>
                    <td>$486</td>
                </tr>
                <tr>
                    <th>Company B</th>
                    <td>$147</td>
                    <td>$1,325</td>
                    <td>$683</td>
                    <td>$524</td>
                </tr>
                <tr>
                    <th>Company C</th>
                    <td>$135</td>
                    <td>$2,342</td>
                    <td>$33</td>
                    <td>$464</td>
                </tr>
                <tr>
                    <th>Company D</th>
                    <td>$164</td>
                    <td>$332</td>
                    <td>$331</td>
                    <td>$438</td>
                </tr>
                <tr>
                    <th>Company E</th>
                    <td>$199</td>
                    <td>$902</td>
                    <td>$336</td>
                    <td>$1,427</td>
                </tr>
            </tbody>
        </table>
        <p class="footnote">*Stated in millions of dollars</p>

fiddle.js

window.onload = function() {
    var sales = new TableSort("sales");
};

fiddle.manifest

name: jsFiddle/Gist TableSort demo
description: jsFiddle demo hosted on Gist 
authors:
  - Gary Smith
title:
  - JS Fiddle - jsFiddle/Gist integration demo - students
resources:
  - /js/empty.js
  - /css/normalize.css
  - https://raw.github.com/gist/1663452/7f6270af1e695cea8198164979d726cae566f026/tablesort.js
normalize_css: no

...

tablesort.js

function TableSort(id) {
    this.tbl = document.getElementById(id);
    this.lastSortedTh = null;
    if (this.tbl && this.tbl.nodeName == "TABLE") {
        var headings = this.tbl.tHead.rows[0].cells;
        for (var i=0; headings[i]; i++) {
            if (headings[i].className.match(/asc|dsc/)) {
                this.lastSortedTh = headings[i];
            }
        }
        this.makeSortable();
    }
}

TableSort.prototype.makeSortable = function () {
    var headings = this.tbl.tHead.rows[0].cells;
    for (var i=0; headings[i]; i++) {
	    headings[i].cIdx = i;
        var a = document.createElement("a");
            a.href = "#";
            a.innerHTML = headings[i].innerHTML;
            a.onclick = function (that) {
                return function () {
                    that.sortCol(this);
                    return false;
                }
            }(this);
        headings[i].innerHTML = "";
        headings[i].appendChild(a);
    }
}

TableSort.prototype.sortCol = function (el) {
    /*
     * Get cell data for column that is to be sorted from HTML table
     */
    var rows = this.tbl.rows;
    var alpha = [], numeric = [];
    var aIdx = 0, nIdx = 0;
    var th = el.parentNode;
    var cellIndex = th.cIdx;
    for (var i=1; rows[i]; i++) {
        var cell = rows[i].cells[cellIndex];
        var content = cell.textContent ? cell.textContent : cell.innerText;
        /*
         * Split data into two separate arrays, one for numeric content and 
         * one for everything else (alphabetic). Store both the actual data
         * that will be used for comparison by the sort algorithm (thus the need
         * to parseFloat() the numeric data) as well as a reference to the 
         * element's parent row. The row reference will be used after the new
         * order of content is determined in order to actually reorder the HTML
         * table's rows.
         */
        var num = content.replace(/(\$|\,|\s)/g, "");
          if (parseFloat(num) == num) { 
            numeric[nIdx++] = {
                value: Number(num),
                row: rows[i]
            }
        } else {
            alpha[aIdx++] = {
                value: content,
                row: rows[i]
            }
        }
    }
    
    /*
     * Sort according to direction (ascending or descending)
     */
    var col = [], top, bottom;
    if (th.className.match("asc")) {
        top = bubbleSort(alpha, -1);
        bottom = bubbleSort(numeric, -1);
        th.className = th.className.replace(/asc/, "dsc");
    } else {
        top = bubbleSort(numeric, 1);
        bottom = bubbleSort(alpha, 1);
        if (th.className.match("dsc")) {
            th.className = th.className.replace(/dsc/, "asc");
        } else {
            th.className += "asc";
        }
    }
    
    /*
     * Clear asc/dsc class names from the last sorted column's th if it isnt the
     * same as the one that was just clicked
     */
    if (this.lastSortedTh && th != this.lastSortedTh) {
        this.lastSortedTh.className = this.lastSortedTh.className.replace(/dsc|asc/g, "");
    }
    this.lastSortedTh = th;
    
    /*
     *  Reorder HTML table based on new order of data found in the col array
     */
    col = top.concat(bottom);
    var tBody = this.tbl.tBodies[0];
    for (var i=0; col[i]; i++) {
        tBody.appendChild(col[i].row);
    }
}

function bubbleSort(arr, dir) {
    // Pre-calculate directional information
    var start, end;
    if (dir === 1) {
        start = 0;
        end = arr.length;
    } else if (dir === -1) {
        start = arr.length-1;
        end = -1;
    }
    
    // Bubble sort: http://en.wikipedia.org/wiki/Bubble_sort
    var unsorted = true;
    while (unsorted) {
        unsorted = false;
        for (var i=start; i!=end; i=i+dir) {
            if (arr[i+dir] && arr[i].value > arr[i+dir].value) {
                var a = arr[i];
                var b = arr[i+dir];
                var c = a;
                arr[i] = b;
                arr[i+dir] = c;
                unsorted = true;
            }
        }
    }
    return arr;
}