JS 计算任意字符串宽度

Lemon学姐

PS: 是宽度不是长度！

由于像素和字体大小，字节（特别是 UTF-8）等限制因素，所以我们不能直接知道一个字符串所占的实际宽度。

这里提供几种比较测量方法：

1、通过Canvas测

/**
 * Uses canvas.measureText to compute and return the width of the given text of given font in pixels.
 * @param {String} text The text to be rendered.
 * @param {String} font The css font descriptor that text is to be rendered with (e.g. "bold 14px verdana").
 * @see https://stackoverflow.com/questions/118241/calculate-text-width-with-javascript/21015393#21015393
function getTextWidth(text, font) {
  // re-use canvas object for better performance
  var canvas = getTextWidth.canvas || (getTextWidth.canvas = document.createElement("canvas"));
  var context = canvas.getContext("2d"); 
  context.font = font;
  var metrics = context.measureText(text);
  return metrics.width;
console.log(getTextWidth("hello there!", "bold 12pt arial"));  // close to 86

2、通过 DOM 测量，这种方法在字符串中含有多个空格时，测出来的宽度会一样，

例如： ''天猫旗舰店 49.67%(tmall)'' 和 ''天猫旗舰店 49.67%(tmall)'' 测出来的宽度都为 165（此值可能会有差异）

function getTextWidth(str = '') {
  const dom = document.createElement('span');
  dom.style.display = 'inline-block';
  dom.textContent = '天猫旗舰店   49.67%(tmall)';
  document.body.appendChild(dom);
  const width = dom.clientWidth;
  console.log(dom.clientWidth);
  document.body.removeChild(dom);
  return width;
}

3、用个 visibility: hidden 的浮动的层来计算字符串宽度。

在添加的 div 容器里把样式设置为和你实际的 div 一样。

<!DOCTYPE html>
  <script src='jquery.min.js'></script>
</head>
    id='labelText' 
    style='color:black; line-height:1.2; white-space: nowrap; position:fixed;
      top:0px; left:0px; display:block; visibility:visible;'
  <script>
    var str = 'Live like you were dying, Love because you do.';
    str = str.substring(0, str.length);
    $('#labelText').css({
      'font-size': '12px',
      'font-family': 'Microsoft YaHei'
    }).html(str);
    var width = $('#labelText').width();
    console.log(width);
  </script>
</body>
</html>

计算高度也一样。

最后别忘了移除额外添加的 div！

Code:

let tCanvas = null;
getTextWidth(text, font = 'normal 12px sans-serif') {
  // re-use canvas object for better performance
  const canvas = tCanvas || (tCanvas = document.createElement('canvas'));
  const context = canvas.getContext('2d');
  context.font = font;
  return context.measureText(text).width;
addStrWidthViaBlank(str, width) {
  // 这个函数只适用于'xxx xx'形式的字符串（即原串就含有空格）
  if (width <= 0 || (this.getTextWidth(str) >= width)) {
    return str;
  let tStr = str;
  let tWidth = 0;
  while (tWidth < width) {
    tStr = tStr.replace(/(.*) /, '$1  ');