计算字体的高度和宽度

注意：你使用的是span，那就用span来计算。你使用的div，就用div来计算,下面是代码：

<div id="num">1000asdasdasfdasfasdsadfasdfsadf
sdfsdfsdafasd
sadfsdafsdfsadf
sdfsdfsdfsd</div>
<script type="text/javascript">
function computeFontSize(str, size, family) {
let spanDom = document.createElement("div");//这里，你测量的文字在哪，就使用那种
spanDom.style.fontSize = size;
spanDom.style.opacity = "0";
spanDom.style.fontFamily = family;
spanDom.style.display = "inline-block";
spanDom.innerHTML = str;
document.body.append(spanDom);
let sizeD = {};
sizeD.width = spanDom.offsetWidth;
sizeD.height = spanDom.offsetHeight;

console.log(window.getComputedStyle(spanDom).height);
spanDom.remove();
return sizeD;

}

let str = "H";
let st = computeFontSize(str, "18px", "Arial");
console.log("方法计算大小: ")
console.log(st);
</script>