js合并table单元格

window.onload = function () {
            var tab = document.getElementById("table1"); //要合并的tableID
            var maxCol = 3, val, count, start;  //maxCol：合并单元格作用到多少列  
            if (tab != null) {
                for (var col = maxCol - 1; col >= 0; col--) {
                    count = 1;
                    val = "";
                    for (var i = 0; i < tab.rows.length; i++) {
                        if (val == tab.rows[i].cells[col].innerHTML) {
                            count++;
                        } else {
                            if (count > 1) { //合并
                                start = i - count;
                                tab.rows[start].cells[col].rowSpan = count;
                                for (var j = start + 1; j < i; j++) {
                                    tab.rows[j].cells[col].style.display = "none";
                                }
                                count = 1;
                            }
                            val = tab.rows[i].cells[col].innerHTML;
                        }
                    }
                    if (count > 1) { //合并，最后几行相同的情况下
                        start = i - count;
                        tab.rows[start].cells[col].rowSpan = count;
                        for (var j = start + 1; j < i; j++) {
                            tab.rows[j].cells[col].style.display = "none";
                        }
                    }
                }
            }
        };