最近做项目时，遇到了一个需求：要求div里文本在两行显示，div的宽度是固定的，如果溢出的话就显示省略号。单行文本的溢出问题，我们都很熟悉，只要添加以下css属性就ok：

  overflow: hidden;
  white-space: nowrap; //段落中文本不换行
  text-overflow: ellipsis;

但是多行文本的溢出怎么处理呢？

• 查了资料之后发现还是有办法的

  在WebKit浏览器或移动端（绝大部分是WebKit内核的浏览器）的页面实现比较简单，可以直接使用WebKit的CSS扩展属性(WebKit是私有属性)-webkit-line-clamp ；注意：这是一个 不规范的属性（unsupported WebKit property），它没有出现在 CSS 规范草案中。-webkit-line-clamp用来限制在一个块元素显示的文本的行数。 为了实现该效果，它需要组合其他的WebKit属性。

• 我们用一下代码即可实现：

    overflow : hidden;
    text-overflow: ellipsis;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;

• 但是这样处理会遇到兼容性问题，在Firefox浏览器上就不起作用。
• 为了解决兼容性问题，有一个clamp.js[https://www.npmjs.com/package…]很好的解决这个问题。

• 为了更好的跟Vue相结合，今天我们就封装一个v-clamp的指令，来方便的解决这个问题。

  // 注册一个全局自定义指令 `v-clamp`
  Vue.directive('clamp', {
    // 当被绑定的元素插入到 DOM 中时……
    update: function (el, binding) {
        function clamp(element, options) {
            options = options || {};
        
            var self = this,
              win = window,
              opt = {
                clamp: options.clamp || 2,
                useNativeClamp: typeof(options.useNativeClamp) != 'undefined' ? options.useNativeClamp : true,
                splitOnChars: options.splitOnChars || ['.', '-', '–', '—', ' '], //Split on sentences (periods), hypens, en-dashes, em-dashes, and words (spaces).
                animate: options.animate || false,
                truncationChar: options.truncationChar || '…',
                truncationHTML: options.truncationHTML
              },
        
              sty = element.style,
              originalText = element.innerHTML,
        
              supportsNativeClamp = typeof(element.style.webkitLineClamp) != 'undefined',
              clampValue = opt.clamp,
              isCSSValue = clampValue.indexOf && (clampValue.indexOf('px') > -1 || clampValue.indexOf('em') > -1),
              truncationHTMLContainer;
        
            if (opt.truncationHTML) {
              truncationHTMLContainer = document.createElement('span');
              truncationHTMLContainer.innerHTML = opt.truncationHTML;
            }
        
        
            // UTILITY FUNCTIONS __________________________________________________________
        
            /**
             * Return the current style for an element.
             * @param {HTMLElement} elem The element to compute.
             * @param {string} prop The style property.
             * @returns {number}
             */
            function computeStyle(elem, prop) {
              if (!win.getComputedStyle) {
                win.getComputedStyle = function(el, pseudo) {
                  this.el = el;
                  this.getPropertyValue = function(prop) {
                    var re = /(\-([a-z]){1})/g;
                    if (prop == 'float') prop = 'styleFloat';
                    if (re.test(prop)) {
                      prop = prop.replace(re, function() {
                        return arguments[2].toUpperCase();
                      });
                    }
                    return el.currentStyle && el.currentStyle[prop] ? el.currentStyle[prop] : null;
                  };
                  return this;
                };
              }
        
              return win.getComputedStyle(elem, null).getPropertyValue(prop);
            }
        
            /**
             * Returns the maximum number of lines of text that should be rendered based
             * on the current height of the element and the line-height of the text.
             */
            function getMaxLines(height) {
              var availHeight = height || element.clientHeight,
                lineHeight = getLineHeight(element);
        
              return Math.max(Math.floor(availHeight / lineHeight), 0);
            }
        
            /**
             * Returns the maximum height a given element should have based on the line-
             * height of the text and the given clamp value.
             */
            function getMaxHeight(clmp) {
              var lineHeight = getLineHeight(element);
              return lineHeight * clmp;
            }
        
            /**
             * Returns the line-height of an element as an integer.
             */
            function getLineHeight(elem) {
              var lh = computeStyle(elem, 'line-height');
              if (lh == 'normal') {
                // Normal line heights vary from browser to browser. The spec recommends
                // a value between 1.0 and 1.2 of the font size. Using 1.1 to split the diff.
                lh = parseInt(computeStyle(elem, 'font-size')) * 1.2;
              }
              return parseInt(lh);
            }
        
        
            // MEAT AND POTATOES (MMMM, POTATOES...) ______________________________________
            var splitOnChars = opt.splitOnChars.slice(0),
              splitChar = splitOnChars[0],
              chunks,
              lastChunk;
        
            /**
             * Gets an element's last child. That may be another node or a node's contents.
             */
            function getLastChild(elem) {
              //Current element has children, need to go deeper and get last child as a text node
              if (elem.lastChild.children && elem.lastChild.children.length > 0) {
                return getLastChild(Array.prototype.slice.call(elem.children).pop());
              }
              //This is the absolute last child, a text node, but something's wrong with it. Remove it and keep trying
              else if (!elem.lastChild || !elem.lastChild.nodeValue || elem.lastChild.nodeValue === '' || elem.lastChild.nodeValue == opt.truncationChar) {
                elem.lastChild.parentNode.removeChild(elem.lastChild);
                return getLastChild(element);
              }
              //This is the last child we want, return it
              else {
                return elem.lastChild;
              }
            }
        
            /**
             * Removes one character at a time from the text until its width or
             * height is beneath the passed-in max param.
             */
            function truncate(target, maxHeight) {
              if (!maxHeight) {
                return;
              }
        
              /**
               * Resets global variables.
               */
              function reset() {
                splitOnChars = opt.splitOnChars.slice(0);
                splitChar = splitOnChars[0];
                chunks = null;
                lastChunk = null;
              }
        
              var nodeValue = target.nodeValue.replace(opt.truncationChar, '');
        
              //Grab the next chunks
              if (!chunks) {
                //If there are more characters to try, grab the next one
                if (splitOnChars.length > 0) {
                  splitChar = splitOnChars.shift();
                }
                //No characters to chunk by. Go character-by-character
                else {
                  splitChar = '';
                }
        
                chunks = nodeValue.split(splitChar);
              }
        
              //If there are chunks left to remove, remove the last one and see if
              // the nodeValue fits.
              if (chunks.length > 1) {
                // console.log('chunks', chunks);
                lastChunk = chunks.pop();
                // console.log('lastChunk', lastChunk);
                applyEllipsis(target, chunks.join(splitChar));
              }
              //No more chunks can be removed using this character
              else {
                chunks = null;
              }
        
              //Insert the custom HTML before the truncation character
              if (truncationHTMLContainer) {
                target.nodeValue = target.nodeValue.replace(opt.truncationChar, '');
                element.innerHTML = target.nodeValue + ' ' + truncationHTMLContainer.innerHTML + opt.truncationChar;
              }
        
              //Search produced valid chunks
              if (chunks) {
                //It fits
                if (element.clientHeight <= maxHeight) {
                  //There's still more characters to try splitting on, not quite done yet
                  if (splitOnChars.length >= 0 && splitChar !== '') {
                    applyEllipsis(target, chunks.join(splitChar) + splitChar + lastChunk);
                    chunks = null;
                  }
                  //Finished!
                  else {
                    return element.innerHTML;
                  }
                }
              }
              //No valid chunks produced
              else {
                //No valid chunks even when splitting by letter, time to move
                //on to the next node
                if (splitChar === '') {
                  applyEllipsis(target, '');
                  target = getLastChild(element);
        
                  reset();
                }
              }
        
              //If you get here it means still too big, let's keep truncating
              if (opt.animate) {
                setTimeout(function() {
                  truncate(target, maxHeight);
                }, opt.animate === true ? 10 : opt.animate);
              } else {
                return truncate(target, maxHeight);
              }
            }
        
            function applyEllipsis(elem, str) {
              elem.nodeValue = str + opt.truncationChar;
            }
        
        
            // CONSTRUCTOR ________________________________________________________________
        
            if (clampValue == 'auto') {
              clampValue = getMaxLines();
            } else if (isCSSValue) {
              clampValue = getMaxLines(parseInt(clampValue));
            }
        
            var clampedText;
            if (supportsNativeClamp && opt.useNativeClamp) {
              sty.overflow = 'hidden';
              sty.textOverflow = 'ellipsis';
              sty.webkitBoxOrient = 'vertical';
              sty.display = '-webkit-box';
              sty.webkitLineClamp = clampValue;
        
              if (isCSSValue) {
                sty.height = opt.clamp + 'px';
              }
            } else {
              var height = getMaxHeight(clampValue);
              if (height <= element.clientHeight) {
                console.log(getLastChild(element));
                clampedText = truncate(getLastChild(element), height);
              }
            }
        
            return {
              'original': originalText,
              'clamped': clampedText
            };
          }
  
         clamp(el,{clamp: 2}) 
  
  
    }
  })
  

  • 其实很简单，仅仅是把clamp.js中的函数搬移了过来。然后就可以像这样来使用：

      <div class="txt" v-clamp>很抱歉！没有搜索到相关模板很抱歉！没有搜索到相关模板很抱歉！没有搜索到相关模板很抱歉！没有搜索到相关模板</div>