方法一：
// Only do anything if jQuery isn't defined
if (typeof jQuery == 'undefined') {
if (typeof $ == 'function') {
// warning, global var
thisPageUsingOtherJSLibrary = true;
}
function getScript(url, success) {
var script = document.createElement('script');
script.src = url;
var head = document.getElementsByTagName('head')[0],
done = false;
// Attach handlers for all browsers
script.onload = script.onreadystatechange = function() {
if (!done && (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete')) {
done = true;
// callback function provided as param
success();
script.onload = script.onreadystatechange = null;
head.removeChild(script);
};
};
head.appendChild(script);
};
getScript('http://ajax.googleapis.com/ajax/libs/jquery/1.4.4/jquery.min.js', function() {
if (typeof jQuery=='undefined') {
// Super failsafe - still somehow failed...
} else {
// jQuery loaded! Make sure to use .noConflict just in case
fancyCode();
if (thisPageUsingOtherJSLibrary) {
// Run your jQuery Code
} else {
// Use .noConflict(), then run your jQuery Code
}
}
});
} else { // jQuery was already loaded
// Run your jQuery Code
};
//該代碼片段來自於: http://hovertree.com/code/
方法二：document.write
var jQueryScriptOutputted = false;
function initJQuery() {
//if the jQuery object isn't available
if (typeof(jQuery) == 'undefined') {
if (! jQueryScriptOutputted) {
//only output the script once..
jQueryScriptOutputted = true;
//output the script (load it from google api)
document.write("<scr" + "ipt type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></scr" + "ipt>");
}
setTimeout("initJQuery()", 50);
} else {
$(function() {
// do anything that needs to be done on document.ready
// don't really need this dom ready thing if used in footer
});
}
}
initJQuery();
//該代碼片段來自於: http://hovertree.com/code