Home > Article > Web Front-end > Summary of js preloading image methods_javascript skills

Summary of js preloading image methods_javascript skills

WBOYOriginal: 2016-05-16 15:55:051235browse

The examples in this article summarize the js preloading image method. Share it with everyone for your reference. The specific analysis is as follows:

1. Pure CSS:

#preload-01 {
background: url(http://domain.tld/image-01.png) no-repeat -9999px -9999px;
}
#preload-02 {
background: url(http://domain.tld/image-02.png) no-repeat -9999px -9999px;
}
#preload-03 {
background: url(http://domain.tld/image-03.png) no-repeat -9999px -9999px;
}

2. JS CSS optimization:

// better image preloading @ http://perishablepress.com/press/2009/12/28/3-ways-preload-images-css-javascript-ajax/
function preloader() {
  if (document.getElementById) {
    document.getElementById("preload-01").style.background = "url(http://domain.tld/image-01.png) no-repeat -9999px -9999px";
    document.getElementById("preload-02").style.background = "url(http://domain.tld/image-02.png) no-repeat -9999px -9999px";
    document.getElementById("preload-03").style.background = "url(http://domain.tld/image-03.png) no-repeat -9999px -9999px";
  }
}
function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      if (oldonload) {
        oldonload();
      }
      func();
    }
  }
}
addLoadEvent(preloader);

3. JS code 1:

<div class="hidden">
  <script type="text/javascript">
    <!--//--><![CDATA[//><!--
      var images = new Array()
      function preload() {
        for (i = 0; i < preload.arguments.length; i++) {
          images[i] = new Image()
          images[i].src = preload.arguments[i]
        }
      }
      preload(
        "http://domain.tld/gallery/image-001.jpg",
        "http://domain.tld/gallery/image-002.jpg",
        "http://domain.tld/gallery/image-003.jpg"
      )
    //--><!]]>
  </script>
</div>

4. JS code 2:

<div class="hidden">
  <script type="text/javascript">
    <!--//--><![CDATA[//><!--
      if (document.images) {
        img1 = new Image();
        img2 = new Image();
        img3 = new Image();
        img1.src = "http://domain.tld/path/to/image-001.gif";
        img2.src = "http://domain.tld/path/to/image-002.gif";
        img3.src = "http://domain.tld/path/to/image-003.gif";
      }
    //--><!]]>
  </script>
</div>

5. JS code optimization 2:

function preloader() {
  if (document.images) {
    var img1 = new Image();
    var img2 = new Image();
    var img3 = new Image();
    img1.src = "http://domain.tld/path/to/image-001.gif";
    img2.src = "http://domain.tld/path/to/image-002.gif";
    img3.src = "http://domain.tld/path/to/image-003.gif";
  }
}
function addLoadEvent(func) {
  var oldonload = window.onload;
  if (typeof window.onload != 'function') {
    window.onload = func;
  } else {
    window.onload = function() {
      if (oldonload) {
        oldonload();
      }
      func();
    }
  }
}
addLoadEvent(preloader);

6. Ajax code 1:

window.onload = function() {
  setTimeout(function() {
    // XHR to request a JS and a CSS
    var xhr = new XMLHttpRequest();
    xhr.open('GET', 'http://domain.tld/preload.js');
    xhr.send('');
    xhr = new XMLHttpRequest();
    xhr.open('GET', 'http://domain.tld/preload.css');
    xhr.send('');
    // preload image
    new Image().src = "http://domain.tld/preload.png";
  }, 1000);
};

7. Ajax code 2:

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 = "http://domain.tld/preload.css";
    // a new JS
    var js = document.createElement("script");
    js.type = "text/javascript";
    js.src = "http://domain.tld/preload.js";
    // preload JS and CSS
    head.appendChild(css);
    head.appendChild(js);
    // preload image
    new Image().src = "http://domain.tld/preload.png";
  }, 1000);
};

I hope this article will be helpful to everyone’s JavaScript programming design.

Statement：

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Previous article：Detailed explanation of the use of acos() method in JavaScript_Basic knowledgeNext article：Detailed explanation of the use of acos() method in JavaScript_Basic knowledge

See more

Summary of js preloading image methods_javascript skills

Related articles