最近遇到一个貌似很简单，但写起来也不简单的问题。对于多行文字，超出...显示。通过css可以实现，但受限于浏览器兼容问题，有时候还需要依赖JS来实现。通过js实现，就需要考虑到文字大小，中英文、数子、标点符号所对应的字节长度不一致，如果考虑的不全面，对于不同的文字内容，总会有点差距。

function bitCompute(content) {
   var total = 0,
    len = arguments[0].length || 0
   for (var i = 0; i < len; i++) {
    if (content[i].charCodeAt() > 255) {
     total += 2;
    } else {
     total += 1;
    }
   }
   return total
}

function complate() {
   var offsetWidth = el.offsetWidth;
   var scrollWidth = el.scrollWidth;
   var gap = scrollWidth - offsetWidth;
   var percent = Math.floor(offsetWidth / scrollWidth * 1e3) / 1e3;
   return {
    gap: gap,
    percent: percent
   }
}

function cut(content) {
   el.innerhtml = content;
   var info = complate(),
    percent = info.percent;
   var total = bitCompute(content).total;
   var showLen = +(total * percent).toFixed(0) - cfg.placeholder;
   content = bitCompute(content, showLen).content;
   return content + cfg.padding;
}
  
function bitCompute(content, maxLen) {
   var total = 0,
    len = arguments[0].length || 0,
    outContent = '';
   for (var i = 0; i < len; i++) {
    if (content[i].charCodeAt() > 255) {
     total += 2;
    } else {
     total += 1;
    }
    if (maxLen && total > maxLen) {
     break;
    }
    outContent += content[i];
   }
   return {
    total: total,
    content: outContent
   }
}

function cutFactory(opt) {
  var cfg = {
   padding: opt.padding || "...",
   classList: opt.classList || [],
   style: opt.style || {},
   debug: opt.debug
  };
  cfg.placeholder = bitCompute(cfg.padding).total;
  var el = doc.createElement("span");
  el.className = cfg.classList.join(" ");
  var customStyles = [];
  for (var styleKey in cfg.style) {
   if (cfg.style.hasOwnProperty(styleKey)) {
    customStyles.push(styleKey + ":" + cfg.style[styleKey]);
   }
  }
  el.style.cssText = "position:absolute;left:0;top:0;background:transparent;color:transparent;height:100%;white-space:nowrap;overflow:visible;border:0;" + (cfg.debug ? "background:white;color:red;" : "") + customStyles.join(";");
  var div = doc.createElement("div");
  div.appendChild(el);
  div.style.cssText = "width:99%;min-height:50px;line-height:50px;position:absolute;left:3px;top:3px;overflow:hidden;outline:0;background:transparent;" + (cfg.debug ? "outline:1px solid red;background:black;" : "");
  doc.body.appendChild(div);
  var css = win.getComputedStyle(el);
  cfg.fontSize = parseFloat(css.fontSize) || 16;
  return function (content) {
   el.innerHTML = content;
   var out = {
    flag: false,
    cut: '',
    all: content,
    last: content
   }
   if (complate().gap > 0) {
    out.flag = true,
    out.last = out.cut = cut(content)
   }
   return out
  }
}

function subStringEL(name, fontSize, width) {
  this.subStringELFns || (this.subStringELFns = {});
  var key = 'key_' + fontSize + '_' + width;
  var fn = this.subStringELFns[key];
  if (!fn) {
   fn = this.subStringELFns[key] = cutFactory({
    style: {
     'font-size': fontSize,
     'width': width
    }
   })
  }
  return fn(name);
}

这样就完美的解决了多行超出...显示的问题了，兼容性很好，而且也能准确截取，灵活方便。希望能帮助到受该问题困扰的同仁，内容中如有不正确之处，烦请指正,不胜感激!

另外附注源码地址：github.com/18822600748/MyJSFactory/blob/main/src/subStrByWidth.js
作者：梦想敲木鱼
https://juejin.cn/post/7026655351004987400