使用带有回调的 javascript 动态加载 css 文件，无需 jQuery

Question

我正在尝试使用 javascript 动态加载 css 文件，并且不能使用任何其他 js 库（例如 jQuery）。

css 文件已加载，但我似乎无法获得回调来为其工作。下面是我正在使用的代码

var callbackFunc = function(){
    console.log('file loaded');     
};
var head = document.getElementsByTagName( "head" )[0];
var fileref=document.createElement("link");
    fileref.setAttribute("rel", "stylesheet");
    fileref.setAttribute("type", "text/css");
    fileref.setAttribute("href", url);

    fileref.onload  = callbackFunc;
    head.insertBefore( fileref, head.firstChild );

使用以下代码添加脚本标记来加载 js 文件可以工作并触发回调：

var callbackFunc = function(){
    console.log('file loaded');     
};

var script = document.createElement("script");

script.setAttribute("src",url);
script.setAttribute("type","text/javascript");

script.onload  = callbackFunc ;

head.insertBefore( script, head.firstChild );

我在这里做错了什么吗？任何其他可以帮助我实现这一目标的方法将不胜感激？

Answer 1

不幸的是，大多数现代浏览器都不支持样式表加载。我通过谷歌搜索找到了一个解决方案。

引用自： http://thudjs .tumblr.com/post/637855087/stylesheet-onload-or-lack-thereof

基础知识

最基本的实现可以通过区区 30 行独立于框架的 JavaScript 代码完成：

function loadStyleSheet( path, fn, scope ) {
   var head = document.getElementsByTagName( 'head' )[0], // reference to document.head for appending/ removing link nodes
       link = document.createElement( 'link' );           // create the link node
   link.setAttribute( 'href', path );
   link.setAttribute( 'rel', 'stylesheet' );
   link.setAttribute( 'type', 'text/css' );

   var sheet, cssRules;
// get the correct properties to check for depending on the browser
   if ( 'sheet' in link ) {
      sheet = 'sheet'; cssRules = 'cssRules';
   }
   else {
      sheet = 'styleSheet'; cssRules = 'rules';
   }

   var interval_id = setInterval( function() {                     // start checking whether the style sheet has successfully loaded
          try {
             if ( link[sheet] && link[sheet][cssRules].length ) { // SUCCESS! our style sheet has loaded
                clearInterval( interval_id );                      // clear the counters
                clearTimeout( timeout_id );
                fn.call( scope || window, true, link );           // fire the callback with success == true
             }
          } catch( e ) {} finally {}
       }, 10 ),                                                   // how often to check if the stylesheet is loaded
       timeout_id = setTimeout( function() {       // start counting down till fail
          clearInterval( interval_id );             // clear the counters
          clearTimeout( timeout_id );
          head.removeChild( link );                // since the style sheet didn't load, remove the link node from the DOM
          fn.call( scope || window, false, link ); // fire the callback with success == false
       }, 15000 );                                 // how long to wait before failing

   head.appendChild( link );  // insert the link node into the DOM and start loading the style sheet

   return link; // return the link node;
}

这将允许您使用 onload 回调函数加载样式表，如下所示：

loadStyleSheet( '/path/to/my/stylesheet.css', function( success, link ) {
   if ( success ) {
      // code to execute if the style sheet was loaded successfully
   }
   else {
      // code to execute if the style sheet failed to successfully
   }
} );

或者，如果您希望回调保持其范围/上下文，您可以执行如下操作：

loadStyleSheet( '/path/to/my/stylesheet.css', this.onComplete, this );

Answer 2

这种普通的 JS 方法适用于所有现代浏览器：

let loadStyle = function(url) {
  return new Promise((resolve, reject) => {
    let link    = document.createElement('link');
    link.type   = 'text/css';
    link.rel    = 'stylesheet';
    link.onload = () => { resolve(); console.log('style has loaded'); };
    link.href   = url;

    let headScript = document.querySelector('script');
    headScript.parentNode.insertBefore(link, headScript);
  });
};

// works in IE 10, 11 and Safari/Chrome/Firefox/Edge
// add an ES6 polyfill for the Promise (or rewrite to use a callback)

Answer 3

前段时间我为此创建了一个库，它的名字是 Dysel，我希望它有帮助

示例：
https://jsfiddle.net/sunrising/qk0ybtnb/

var googleFont = 'https://fonts.googleapis.com/css?family=Lobster';
var jquery = 'https://code.jquery.com/jquery.js';
var bootstrapCss = 'https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css';
var bootstrapJs = 'https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js';
var smokeCss = 'https://rawgit.com/alfredobarron/smoke/master/dist/css/smoke.min.css';
var smokeJs = 'https://rawgit.com/alfredobarron/smoke/master/dist/js/smoke.min.js';

// push links into an array in the correct order
var extRes = [];
extRes.push(googleFont);
extRes.push(bootstrapCss);
extRes.push(smokeCss);
extRes.push(jquery);
extRes.push(bootstrapJs);
extRes.push(smokeJs);

// let this happen
dysel({
  links: extRes,
  callback: function() {
    alert('everything is now loaded, this is awesome!');
  }, // optional
  nocache: false, // optional
  debug: false // optional
});

Answer 4

您可以在 html 文件中创建一个空的 css 链接，并为该链接指定一个 ID。例如

<link id="stylesheet_css" rel="stylesheet" type="text/css" href="css/dummy.css?"/>

，然后使用 ID 名称调用它并更改“href”属性

Answer 5

yepnope.js 可以加载 CSS 并在完成时运行回调。例如

yepnope([{
  load: "styles.css",
  complete: function() {
    console.log("oooooo. shiny!");
  }
}]);

Answer 6

我们是这样做的。通过使用“requestAnimationFrame”（如果无效，则回退到简单的“load”事件）。

顺便说一句，这是谷歌在其“页面速度”手册中推荐的方式：
https://developers.google.com/speed/docs/insights/OptimizeCSSDelivery

<script>
    function LoadCssFile(cssPath) {
        var l = document.createElement('link'); l.rel = 'stylesheet'; l.href = cssPath;
        var h = document.getElementsByTagName('head')[0]; h.parentNode.insertBefore(l, h);
    }
    var cb = function() {
        LoadCssFile('file1.css');
        LoadCssFile('file2.css');
    };
    var raf = window.requestAnimationFrame || window.mozRequestAnimationFrame || window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
    if (raf) raf(cb);
    else window.addEventListener('load', cb);
</script>

Answer 7

老问题的新答案：

您可以简单地使用 AJAX 请求 CSS 文件的文本并将其放入

这是我想出的一个脚本：

/**
 * Given a URL for a JS or CSS file, this function will
 * load the asset and return a Promise which will reject
 * on error or resolve when the asset is loaded.
 */
function loadAsset(url){
  return new Promise(async (resolve, reject)=>{
    var asset;
    if(url.trim().substr(-3).toLowerCase() === '.js'){
      asset = document.createElement('script');
      asset.addEventListener('load', resolve);
      asset.addEventListener('error', reject);
      document.head.appendChild(asset);
      asset.setAttribute('src', url);
    }else{
      var styles = await fetch(url)
        .then(c=>c.text())
        .catch(reject);
      asset = document.createElement('style');
      asset.appendChild(document.createTextNode(styles));
      document.head.appendChild(asset);
      resolve();
    }
  });
}