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这篇文章主要介绍了如何通过封装一个v-clamp的指令处理多行文本溢出，具有一定借鉴价值，感兴趣的朋友可以参考下，希望大家阅读完这篇文章之后大有收获，下面让小编带着大家一起了解一下。
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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;
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：