What makes this the fastest JavaScript for printing 1 to 1,000,000 (separated by spaces) in a web browser?

<html>
<head>
<script type="text/javascript">
    function printAllNumberBuffered(n, bufferSize)
    {
    	var startTime = new Date();

        var oRuntime = document.getElementById("divRuntime");
    	var oNumbers = document.getElementById("divNumbers");

    	var i = 0;
        var currentNumber;
    	var pass = 0;
    	var numArray = new Array(bufferSize);

    	for(currentNumber = 1; currentNumber <= n; currentNumber++)
    	{
    		numArray[i] = currentNumber;

    		if(currentNumber % bufferSize == 0 && currentNumber > 0)
    		{
    			oNumbers.textContent += numArray.join(' ');
    			i = 0;
    		}
    		else
    		{
    			i++;
    		}
    	}

    	if(i > 0)
    	{
    	    numArray.splice(i - 1, bufferSize - 1);
    		oNumbers.textContent += numArray.join(' ');
    	}

    	var endTime = new Date();

    	oRuntime.innerHTML += "<div>Number: " + n + " Buffer Size: " + bufferSize + " Runtime: " + (endTime - startTime) + "</div>";
    }

    function PrintNumbers()
    {
        var oNumbers = document.getElementById("divNumbers");
    	var tbNumber = document.getElementById("tbNumber");
    	var tbBufferSize = document.getElementById("tbBufferSize");

    	var n = parseInt(tbNumber.value);
    	var bufferSize = parseInt(tbBufferSize.value);

    	oNumbers.textContent = "";

    	printAllNumberBuffered(n, bufferSize);
    }
</script>
</head>
<body>
<table  border="1">
    <tr>
    	<td colspan="2">
    		<div>Number:&nbsp;<input id="tbNumber" type="text" />Buffer Size:&nbsp;<input id="tbBufferSize" type="text" /><input type="button" value="Run" onclick="PrintNumbers();" /></div>
    	</td>
    </tr>
    <tr>
    	<td style="vertical-align:top" width="30%">
    		<div  id="divRuntime"></div>
    	</td>
    	<td width="90%">
    		<div id="divNumbers"></div>
    	</td>
    </tr>
</table>
</body>
</html>