Convert HTMLTableElement (with rowSpan and colSpan) into a JavaScript Array

HTMLTableElement.prototype.fp_toTable.html

<script type="text/javascript">
	HTMLTableElement.prototype.fp_toTable = function(nullvalue = null) {
		var columnCount = Array.from(this.rows).map(row => Array.from(row.cells).reduce((sum, cell) => sum + cell.colSpan, 0)).reduce((max, row) => Math.max(max, row), 0);
		var itemCount = Array.from(this.rows).reduce((rsum, row) => rsum + Array.from(row.cells).reduce((csum, cell) => csum + (cell.colSpan * cell.rowSpan), 0), 0);
		var rowCount = itemCount / columnCount;
		var items = Array.apply(null, Array(itemCount));
		tds = Array.from(this.getElementsByTagName('td'));
		for(var i=0, ii=0; i<tds.length; i++, ii=items.indexOf(undefined, i)) {
			items[ii] = tds[i].innerText;
			for(var j=0;j<tds[i].colSpan;j++) {
				for(var k=0;k<tds[i].rowSpan;k++) {
					if(j||k) {
						items[ii + j + (k * columnCount)] = nullvalue;
					}
				}
			}
		}
		return Array.from(Array(rowCount).keys()).map(r => items.slice(r*columnCount, (r+1)*columnCount));
	};
</script>

<style type="text/css">td{vertical-align:top;}</style>

<table border="1" id="table">
	<tr>
		<td>A</td>
		<td>B</td>
		<td>C</td>
	</tr>
	<tr>
		<td colspan="2" rowspan="2">D</td>
		<td>E</td>
	</tr>
	<tr>
		<td>F</td>
	</tr>
	<tr>
		<td>G</td>
		<td rowspan="3" colspan="2">H</td>
	</tr>
	<tr>
		<td>I</td>
	</tr>
	<tr>
		<td>J</td>
	</tr>
</table>

<script type="text/javascript">
	var table = document.getElementById('table');
	console.table(table.fp_toTable());
</script>