ExtJs--15--Ext.is*各种类型推断的方法,简单看源代码就能够明确了

        /**
         * Returns true if the passed value is empty, false otherwise. The value is deemed to be empty if it is either:
         *
         * - `null`
         * - `undefined`
         * - a zero-length array
         * - a zero-length string (Unless the `allowEmptyString` parameter is set to `true`)
         *
         * @param {Object} value The value to test
         * @param {Boolean} allowEmptyString (optional) true to allow empty strings (defaults to false)
         * @return {Boolean}
         * @markdown
         */
        isEmpty: function(value, allowEmptyString) {
            return (value === null) || (value === undefined) || (!allowEmptyString ? value === '' : false) || (Ext.isArray(value) && value.length === 0);
        },

        /**
         * Returns true if the passed value is a JavaScript Array, false otherwise.
         *
         * @param {Object} target The target to test
         * @return {Boolean}
         * @method
         */
        isArray: ('isArray' in Array) ? Array.isArray : function(value) {
            return toString.call(value) === '[object Array]';
        },

        /**
         * Returns true if the passed value is a JavaScript Date object, false otherwise.
         * @param {Object} object The object to test
         * @return {Boolean}
         */
        isDate: function(value) {
            return toString.call(value) === '[object Date]';
        },

        /**
         * Returns true if the passed value is a JavaScript Object, false otherwise.
         * @param {Object} value The value to test
         * @return {Boolean}
         * @method
         */
        isObject: (toString.call(null) === '[object Object]') ?
        function(value) {
            // check ownerDocument here as well to exclude DOM nodes
            return value !== null && value !== undefined && toString.call(value) === '[object Object]' && value.ownerDocument === undefined;
        } :
        function(value) {
            return toString.call(value) === '[object Object]';
        },

        /**
         * @private
         */
        isSimpleObject: function(value) {
            return value instanceof Object && value.constructor === Object;
        },
        /**
         * Returns true if the passed value is a JavaScript 'primitive', a string, number or boolean.
         * @param {Object} value The value to test
         * @return {Boolean}
         */
        isPrimitive: function(value) {
            var type = typeof value;

            return type === 'string' || type === 'number' || type === 'boolean';
        },

        /**
         * Returns true if the passed value is a JavaScript Function, false otherwise.
         * @param {Object} value The value to test
         * @return {Boolean}
         * @method
         */
        isFunction:
        // Safari 3.x and 4.x returns 'function' for typeof <NodeList>, hence we need to fall back to using
        // Object.prototype.toString (slower)
        (typeof document !== 'undefined' && typeof document.getElementsByTagName('body') === 'function') ? function(value) {
            return toString.call(value) === '[object Function]';
        } : function(value) {
            return typeof value === 'function';
        },

        /**
         * Returns true if the passed value is a number. Returns false for non-finite numbers.
         * @param {Object} value The value to test
         * @return {Boolean}
         */
        isNumber: function(value) {
            return typeof value === 'number' && isFinite(value);
        },

        /**
         * Validates that a value is numeric.
         * @param {Object} value Examples: 1, '1', '2.34'
         * @return {Boolean} True if numeric, false otherwise
         */
        isNumeric: function(value) {
            return !isNaN(parseFloat(value)) && isFinite(value);
        },

        /**
         * Returns true if the passed value is a string.
         * @param {Object} value The value to test
         * @return {Boolean}
         */
        isString: function(value) {
            return typeof value === 'string';
        },

        /**
         * Returns true if the passed value is a boolean.
         *
         * @param {Object} value The value to test
         * @return {Boolean}
         */
        isBoolean: function(value) {
            return typeof value === 'boolean';
        },

        /**
         * Returns true if the passed value is an HTMLElement
         * @param {Object} value The value to test
         * @return {Boolean}
         */
        isElement: function(value) {
            return value ? value.nodeType === 1 : false;
        },

        /**
         * Returns true if the passed value is a TextNode
         * @param {Object} value The value to test
         * @return {Boolean}
         */
        isTextNode: function(value) {
            return value ? value.nodeName === "#text" : false;
        },

        /**
         * Returns true if the passed value is defined.
         * @param {Object} value The value to test
         * @return {Boolean}
         */
        isDefined: function(value) {
            return typeof value !== 'undefined';
        },

        /**
         * Returns true if the passed value is iterable, false otherwise
         * @param {Object} value The value to test
         * @return {Boolean}
         */
        isIterable: function(value) {
            var type = typeof value,
                checkLength = false;
            if (value && type != 'string') {
                // Functions have a length property, so we need to filter them out
                if (type == 'function') {
                    // In Safari, NodeList/HTMLCollection both return "function" when using typeof, so we need
                    // to explicitly check them here.
                    if (Ext.isSafari) {
                        checkLength = value instanceof NodeList || value instanceof HTMLCollection;
                    }
                } else {
                    checkLength = true;
                }
            }
            return checkLength ? value.length !== undefined : false;
        }