直接调用方法就可
console.log(this.textSize("15px", "Arial", "字符串获取宽度和高度"))

textSize(fontSize, fontFamily, text) {
      var span = document.createElement("span");
      var result = {};
      result.width = span.offsetWidth;
      result.height = span.offsetHeight;
      span.style.visibility = "hidden";
      span.style.fontSize = fontSize;
      span.style.fontFamily = fontFamily;
      span.style.display = "inline-block";
      document.body.appendChild(span);
      if (typeof span.textContent != "undefined") {
        span.textContent = text;
      } else {
        span.innerText = text;
      }
      result.width =
        parseFloat(window.getComputedStyle(span).width) - result.width;
      result.height =
        parseFloat(window.getComputedStyle(span).height) - result.height;
      return result;
    },