jquery的工具方法isFunction/isArray/isWindow/isNumeric/isPlainObject/isEmptyObject

isFunction : 是否函数

isArray : 是否数组

isWindow : 是否window

isNumeric : 是否数字

type : 数据类型方法

isPlainObject : 是否对象字面量

isEmptyObject : 是否空对象

var core_toString = Object.prototype.toString,
    class2type = {};

// Populate the class2type map
jQuery.each("Boolean Number String Function Array Date RegExp Object".split(" "), function(i, name) {
    class2type[ "[object " + name + "]" ] = name.toLowerCase();
});

jQuery.extend({

    ......................

    isFunction: function( obj ) {
        return jQuery.type(obj) === "function";
    },

    isArray: Array.isArray || function( obj ) {
        return jQuery.type(obj) === "array";
    },

    isWindow: function( obj ) {
         //obj.window意思是window.window，前者是全局对象，后者是浏览器窗口
        return obj != null && obj == obj.window;
    },

    isNumeric: function( obj ) {
         //isFinite判断是否为有限的数字
        return !isNaN( parseFloat(obj) ) && isFinite( obj );
    },

    type: function( obj ) {
        return obj == null ?
            String( obj ) :
            class2type[ core_toString.call(obj) ] || "object";
    },

    isPlainObject: function( obj ) {
        // Must be an Object.
        // Because of IE, we also have to check the presence of the constructor property.
        // Make sure that DOM nodes and window objects don't pass through, as well
        if ( !obj || jQuery.type(obj) !== "object" || obj.nodeType || jQuery.isWindow( obj ) ) {
            return false;
        }

        try {
            // Not own constructor property must be Object
            if ( obj.constructor &&
                !core_hasOwn.call(obj, "constructor") &&
                !core_hasOwn.call(obj.constructor.prototype, "isPrototypeOf") ) {
                return false;
            }
        } catch ( e ) {
            // IE8,9 Will throw exceptions on certain host objects #9897
            return false;
        }

        // Own properties are enumerated firstly, so to speed up,
        // if last one is own, then all properties are own.

        var key;
        for ( key in obj ) {}

        return key === undefined || core_hasOwn.call( obj, key );
    },

    isEmptyObject: function( obj ) {
        var name;
        for ( name in obj ) {
            return false;
        }
        return true;
    },

    ...............

});