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jQuery notes - tool functions - jQuery logo

巴扎黑Original: 2017-07-08 11:10:581214browse

jQuery defines many tool functions. The namespace of these functions is $, but they do not operate on the wrapper set. Users can regard it as a top-level function. The difference is that they are defined on the $ instance. , rather than being defined on the window instance, similar to a static type function.

Generally speaking, the main task of the tool function is to operate JavaScript objects except DOM, or perform some non-object related operations.

jQuery provides developers with some useful customer information through the variables defined on $. Through these flag information, the functions of the current browser can be easily detected, so that users can make decisions based on this information.

These flag information include: jQuery.browser, jQuery.boxModel and jQuery.support

1. Detect users Agent

Browser detection method:

1. String detection method: Detect based on the return value of the navigator.userAgent property. However, jQuery no longer supports this method from version 1.3. The reason is: it is troublesome to use and goes against the smart features of jQuery.

2. Feature detection method: Determine the operation method based on whether the browser supports specific functions.

Non -precise, the safest

If you don't care about the identity of the browser and only care about the execution ability of the browser, then this method is enough.

For example:

            var a;
            if(document.getElementsByName){               //如果存在getElementsByName，则使用该方法获取a元素
                a = document.getElementsByName("a");
            }
            else if(document.getElementsByTagName){       //如果存在getElementsByTagName，则使用该方法获取a元素
                a = document.getElementsByTagName("a")
            }

When using an object, method or attribute, you can first detect whether the current browser supports it. In a logical expression, if the browser supports it, the object, property or method will be returned, and JavaScript will force these objects or members to be converted to true. If it is not supported, undefined will be returned, and JavaScript will automatically convert it to false.

Note: When detecting a method or function, do not add parentheses, otherwise the JavaScript interpreter will call the method or function, and if the specified function does not exist, a compilation error will occur.

Detect browser type:

js: var browser = navigator.userAgent;

jQuery: browser attribute. Allows detection of the 4 most popular browser classes, such as Internet Explorer, Mozilla, Webkit, Opera, and each version information flag.

Available flags include: webkit, safari (deprecated), opera, msie and mozilla.

1.9 has been removed. Used to return information related to the browser currently used by the user. ## because it is based on navigator.userAgent attribute to determine

browser information

, so its identification is not necessarily accurate. 2. Detection box model

jQuery.boxModel: Flag OK Gets which box model the current page uses. true: W3C standard box model; false: IE browser box model

jQuery1.0 新增该静态属性；1.3中被标记已过时，请使用 jQuery.support.boxModel替代；1.8中被移除。

除IE浏览器外，其他浏览器都支持W3C标准盒模型，而IE浏览器能够根据页面模式（严格模式或怪异模式）有选择的使用不同类型的盒模型。如果页面顶部声明了文档类型（DOCTYPE），则IE也会采用严格模式，即W3C标准盒模型解析元素。如果文档当中没有包含文档类型（DOCTYPE），或者包含了无法识别的文档类型声明，即会以怪异模式显示，并按IE的传统的盒模型来解析元素。

IE传统的盒模型和W3C标准盒模型的区别：

1.IE传统盒模型：width和height属性包含内边距和边框宽度

2.W3C标准盒模型：width和height属性不包含内边距和边框宽度

用JavaScript检测盒模型：

<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>检测盒模型[JavaScript]</title>
    <script src="js/jquery2.1.3.min.js"></script>
    <script type="text/javascript">
        function isBoxModel(){
            var p = document.createElement("p");
            p.style.width = p.style.paddingLeft = "1px";
            document.body.appendChild(p);
            var width = p.offsetWidth;
            p.style.display = "none";
            document.body.removeChild(p);
            return width === 2;
        }
        window.onload = function(){
            alert(isBoxModel() && "支持W3C标准盒模型" || "支持IE的怪异解析模式");
        }
    </script>
</head>
<body>
</body>
</html>

三、检测功能或缺陷

jQuery的support属性：

返回一个Object对象，在该对象中包含了一组属性，他们代表了不同的浏览器功能或缺陷的存在的合集。

该对象的属性并不是一成不变的，jQuery也并不保证指定的属性在未来的版本中一定可用，这些属性主要供插件或内核开发人员使用。

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