使用 js 获取文本宽度
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;
}
通过创建 div,然后获取宽度
function getTextWidth(text, font) {
  var span = document.createElement("span");
  span.style.font = font;
  span.innerHTML = text;
  document.body.appendChild(span);
  var width = span.offsetWidth;
  document.body.removeChild(span);
  return width;
}