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javascript中延遲加載的7種方法實(shí)現(xiàn)

更新時(shí)間：2025年01月13日 11:10:55 作者：baoeni

在web前端開(kāi)發(fā)中,性能優(yōu)化一直是一個(gè)非常重要的話題,JavaScript中延遲加載的方式有很多種,本文就來(lái)介紹了javascript中延遲加載的7種方法實(shí)現(xiàn),具有一定的參考價(jià)值,感興趣的可以了解一下

1. DOM

head append script tag

window.onload = function() {
    setTimeout(function(){

        // reference to <head>
        var head = document.getElementsByTagName('head')[0];

        // a new CSS
        var css = document.createElement('link');
        css.type = "text/css";
        css.rel = "stylesheet";
        css.href = "new.css";

        // a new JS
        var js = document.createElement("script");
        js.type = "text/javascript";
        js.src = "new.js";

        // preload JS and CSS
        head.appendChild(css);
        head.appendChild(js);

        // preload image
        new Image().src = "new.png";

    }, 1000);
};

2. document.write

<script language="javascript" type="text/javascript">
        function include(script_filename) {
            document.write('<' + 'script');
            document.write(' language="javascript"');
            document.write(' type="text/javascript"');
            document.write(' src="' + script_filename + '">');
            document.write('</' + 'script' + '>');
        }

        var which_script = '1.js';
        include(which_script);
        </script>

3. Iframe

和第一種類似，但是script tag是放到iframe的document里面。

window.onload = function() {
    setTimeout(function(){

        // create new iframe
        var iframe = document.createElement('iframe');
        iframe.setAttribute("width", "0");
        iframe.setAttribute("height", "0");
        iframe.setAttribute("frameborder", "0");
        iframe.setAttribute("name", "preload");
        iframe.id = "preload";
        iframe.src = "about:blank";
        document.body.appendChild(iframe);

        // gymnastics to get reference to the iframe document
        iframe = document.all ? document.all.preload.contentWindow : window.frames.preload;
        var doc = iframe.document;
        doc.open(); doc.writeln("<html><body></body></html>"); doc.close(); 

        // create CSS
        var css = doc.createElement('link');
        css.type = "text/css";
        css.rel = "stylesheet";
        css.href = "new.css";

        // create JS
        var js = doc.createElement("script");
        js.type = "text/javascript";
        js.src = "new.js";

        // preload CSS and JS
        doc.body.appendChild(css);
        doc.body.appendChild(js);

        // preload IMG
        new Image().src = "new.png";

    }, 1000);
};

4. Iframe static page

直接把需要加載東西放到另一個(gè)頁(yè)面中

window.onload = function() {
    setTimeout(function(){

        // create a new frame and point to the URL of the static
        // page that has all components to preload
        var iframe = document.createElement('iframe');
        iframe.setAttribute("width", "0");
        iframe.setAttribute("height", "0");
        iframe.setAttribute("frameborder", "0");
        iframe.src = "preloader.html";
        document.body.appendChild(iframe);

    }, 1000);
};