在我的 HTML 源代码中，我有一个如下代码块（我在此页面上使用 showdown 和 highlight.js）：
<pre><code class="cpp">
double myNumber = (double)4;
</code></pre>
我的问题是第一个换行符仍然是“代码”块的一部分。这可能是因为封闭的“pre”块，但我需要它，因为 highlight.js 需要它（显然 HTML5 标准也推荐它）。代码呈现如下（注意前导换行符）：
所以我的问题是，使用 css、javascript 或 jquery，如何从像这样的“代码”块中删除前导或尾随换行符？
你可以使用这个技巧：
pre:first-line {
line-height: 0;
}
这是使用 Javascript 的另一种方法，它也解决了这个问题：
<script>
window.onload = function (){
// remove leading linebreaks from code blocks.
var pre = document.getElementsByTagName("code");
for (var i = 0, len = pre.length; i < len; i++) {
var text = pre[i].firstChild.nodeValue;
pre[i].firstChild.nodeValue = text.replace(/^\n+|\n+$/g, "");
}
}
</script>
其他人发布了这个，然后删除了他们的答案，但我认为它值得保留。
这就是pre默认情况下的工作方式：它尊重换行符和空格。如果您不想渲染换行符，则必须将其删除。如果您关心源的外观，请直接将其从源中删除或将其注释掉。
<pre><code class="cpp"><!--
-->double myNumber = (double)4;<!--
--></code></pre>
我只是在荧光笔开始之前手动删除它们。
const trimLine = node =>
node.firstChild.nodeValue = node.firstChild.nodeValue.replace(/^\n+|\n+$/g, "");
window.onload = function () {
Array.prototype.slice
.call(document.getElementsByTagName("code"), 0)
.map(trimLine);
hljs.initHighlightingOnLoad();
}演示：http: //jsfiddle.net/WjVVs/4/。
在 PC 上使用 Chrome 和 FF 进行了测试。将插件应用于元素时，它在 IE 9 中不起作用code（应用于元素时似乎可以正常工作pre）。我找不到合适的解决方法，但请随时发表评论/更新。
这是另一个答案的修改版本。这个插件试图去除由文档的自然流动引起的额外缩进。我已经对其进行了修改，使其在前导空白方面更加智能。
如果它工作正常，您应该会看到如下内容：
$("code").prettyPre(); // any selector here
<div>
<pre><code class="cpp">
double myNumber = (double)4;
// another line
// another line
// this is purposely indented further
for( var i = 0; i < 100; i++ ){
}
</code></pre>
</div>
(function( $ ) {
$.fn.prettyPre = function( method ) {
var defaults = {
ignoreExpression: /\s/ // what should be ignored?
};
var methods = {
init: function( options ) {
this.each( function() {
var context = $.extend( {}, defaults, options );
var $obj = $( this );
var usingInnerText = true;
var text = $obj.get( 0 ).innerText;
// some browsers support innerText...some don't...some ONLY work with innerText.
if ( typeof text == "undefined" ) {
text = $obj.html();
usingInnerText = false;
}
// use the first line as a baseline for how many unwanted leading whitespace characters are present
var superfluousSpaceCount = 0;
var pos = 0;
var currentChar = text.substring( 0, 1 );
while ( context.ignoreExpression.test( currentChar ) ) {
if(currentChar !== "\n"){
superfluousSpaceCount++;
}else{
superfluousSpaceCount = 0;
}
currentChar = text.substring( ++pos, pos + 1 );
}
// split
var parts = text.split( "\n" );
var reformattedText = "";
// reconstruct
var length = parts.length;
for ( var i = 0; i < length; i++ ) {
// remove leading whitespace (represented by an empty string)
if(i === 0 && parts[0]=== ""){
continue;
}
// cleanup, and don't append a trailing newline if we are on the last line
reformattedText += parts[i].substring( superfluousSpaceCount ) + ( i == length - 1 ? "" : "\n" );
}
// modify original
if ( usingInnerText ) {
$obj.get( 0 ).innerText = reformattedText;
}
else {
// This does not appear to execute code in any browser but the onus is on the developer to not
// put raw input from a user anywhere on a page, even if it doesn't execute!
$obj.html( reformattedText );
}
} );
}
}
if ( methods[method] ) {
return methods[method].apply( this, Array.prototype.slice.call( arguments, 1 ) );
}
else if ( typeof method === "object" || !method ) {
return methods.init.apply( this, arguments );
}
else {
$.error( "Method " + method + " does not exist on jQuery.prettyPre." );
}
}
} )( jQuery );
这些函数使用一个类（添加到pre）来删除前导和尾随空格
function removeWhitespace(indent) {
// Get a list of all elements that need whitespace removed by indent value (will have class `indent-X`)
// List may be 0 long - loop simply doesn't run
var preElements = document.getElementsByClassName('indent-'+indent);
for (i = 0; i < preElements.length; i++) {
preElements[i].innerHTML = preElements[i].innerHTML.split('\n'+' '.repeat(indent)).join('\n').split('\n'+' '.repeat(indent-2)+'</code>').join('</code>').split("\n").slice(1,-1).join("\n");
//split('\n'+' '.repeat(indent)).join('\n') -- Split at every newline followed by X spaces. Then join together with the newlines.
// .split('\n'+' '.repeat(indent-2)+'</code>').join('</code>') -- The lastline will have 2 less spaces, so remove those, and the newline at the end. Add the tag back in.
//.split("\n").slice(1,-2).join("\n"); -- Remove the first and last lines.
}
}
function removeWhitespaces() {
// Loop over all indents, 2 to 40
for (indent = 2; indent <= 40; indent+=2) {
removeWhitespace(indent);
}
}
只需将要删除的空格数量indent-X的类添加到.Xpre
function removeWhitespace(indent) {
// Get a list of all elements that need indent removed by indent value (will have class `indent-X`)
// List may be 0 long - loop simply doesn't run
var preElements = document.getElementsByClassName('indent-' + indent);
for (i = 0; i < preElements.length; i++) {
preElements[i].innerHTML = preElements[i].innerHTML.split('\n' + ' '.repeat(indent)).join('\n').split('\n' + ' '.repeat(indent - 2) + '</code>').join('</code>').split("\n").slice(1, -2).join("\n");
//split('\n'+' '.repeat(indent)).join('\n') -- Split at every newline followed by X spaces. Then join together with the newlines.
// .split('\n'+' '.repeat(indent-2)+'</code>').join('</code>') -- The lastline will have 2 less spaces, so remove those, and the newline at the end. Add the tag back in.
//.split("\n").slice(1,-1).join("\n"); -- Remove the first and last lines.
// Remove the clickme element.
document.getElementById('clickme').innerHTML = '';
}
}
function removeWhitespaces() {
// Loop over all indents, 2 to 40
for (indent = 2; indent <= 40; indent += 2) {
removeWhitespace(indent);
}
}.indent-14 {
background-color: #ccc;
}<body>
<div id="clickme" onclick="removeWhitespaces()">
Click Me
</div>
<pre class="indent-14">
<code>
function createCORSRequest(method, url) {
var request = new XMLHttpRequest();
if ('withCredentials' in request) {
request.open(method, url, true);
} else if (typeof XDomainRequest != 'undefined') {
request = new XDomainRequest();
request.open(method, url);
} else {
request = null;
}
return request;
}
</code>
</pre>
</body>