js中，怎么计算一个字符串宽度？

http://bbs.csdn.net/topics/300032210

function textSize(fontSize, text) {
    var span = document.createElement("span");
    var result = {};
    result.width = span.offsetWidth;
    result.height = span.offsetWidth;
    span.style.visibility = "hidden";
    document.body.appendChild(span);
    if (typeof span.textContent != "undefined")
        span.textContent = text;
    else span.innerText = text;
    result.width = span.offsetWidth - result.width;
    result.height = span.offsetHeight - result.height;
    span.parentNode.removeChild(span);
    return result;
}

var size = textSize("9px", "囧");
alert("宽：" + size.width + " 高：" + size.height);

http://bbs.csdn.net/topics/390496387

<style>
.content{font-size:20px}
#dvCompute{position:absolute;visibility:hidden;}
</style>
<div class="content" id="dvCompute"></div>
<script>
    function Compute(v) {
        var d = document.getElementById('dvCompute');
        d.innerHTML = v;
        return { w: d.offsetWidth, h: d.offsetHeight };
    }
    window.onload = function () {
        var p = Compute('要计算的内容aaaaaaaaaaaaaaaaaaaaaaaaaaaa<br/>123132');
        alert(p.w + '\n' + p.h);
        var p = Compute('要计算的内容aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa<br/>123132<br/>123132');
        alert(p.w + '\n' + p.h);
    }
</script>