HTML5 Canvas ( 文字的度量 ) measureText

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>canvas</title>
    <script type="text/javascript" src="../js/jQuery.js"></script>
    <style type="text/css">
        *{
            margin: 0;
            padding: 0;
            outline: none;
            border: none;
        }
        #canvas{
            width: 7rem;
            margin: .25rem 0 0 1.5rem;
            border: 1px solid black;
        }
    </style>
</head>
<body>
    <canvas id="canvas" width="1000" height="600"></canvas>
</body>
</html>
<script type="text/javascript">
    /**
     * rem 布局初始化
     */
    $('html').css('font-size', $(window).width()/10);
    /**
     * 获取 canvas 画布
     * 获取 canvas 绘图上下文环境
     */
    var canvas = $('#canvas')[0];
    var cxt = canvas.getContext('2d');

    /**
     * 文字的度量
     * measureText(字符串)
     * 注意在使用前设置好对应的 font 属性才能准确获取文字的长度
     */

    cxt.fillStyle = "blue";
    cxt.font = "bold 40px sans-serif";

    var textWidth = cxt.measureText("Hello Canvas");
    alert(textWidth.width);
</script>