深入學習jquery原始碼之arguments

js 中的函式其實是物件，函式名是對 Function 物件的引用，arguments這個物件不能顯式建立，arguments物件只有函式開始時才可用。

每建立一個函式，該函式就會隱式建立一個arguments物件，他包含有實際傳入引數的資訊。

length   檢測實際傳入引數的個數
callee   對本身的呼叫
訪問傳入引數的具體的值。([下標])

引數個數不確定所以就直接呼叫arguments物件訪問傳遞的引數

jQuery給自己擴充套件屬性的方法，extend方法掛載在jQuery和jQuery.fn兩個不同物件上方法，但在jQuery內部程式碼實現的是相同的，只是功能卻不太一樣；

	    jQuery.fn = jQuery.prototype = {
        // The current version of jQuery being used
        jquery: version,

        constructor: jQuery,

        // Start with an empty selector
        selector: "",

        // The default length of a jQuery object is 0
        length: 0,

        toArray: function () {
            return slice.call(this);
        },

        // Get the Nth element in the matched element set OR
        // Get the whole matched element set as a clean array
        get: function (num) {
            return num != null ?

                // Return just the one element from the set
                (num < 0 ? this[num + this.length] : this[num]) :

                // Return all the elements in a clean array
                slice.call(this);
        },

        // Take an array of elements and push it onto the stack
        // (returning the new matched element set)
        pushStack: function (elems) {

            // Build a new jQuery matched element set
            var ret = jQuery.merge(this.constructor(), elems);

            // Add the old object onto the stack (as a reference)
            ret.prevObject = this;
            ret.context = this.context;

            // Return the newly-formed element set
            return ret;
        },

        // Execute a callback for every element in the matched set.
        // (You can seed the arguments with an array of args, but this is
        // only used internally.)
        each: function (callback, args) {
            return jQuery.each(this, callback, args);
        }
		
		// For internal use only.
        // Behaves like an Array's method, not like a jQuery method.
        push: push,
        sort: deletedIds.sort,
        splice: deletedIds.splice
    };
	
	    jQuery.extend = jQuery.fn.extend = function () {
        var src, copyIsArray, copy, name, options, clone,
            target = arguments[0] || {},
            i = 1,
            length = arguments.length,
            deep = false;

        // Handle a deep copy situation
        if (typeof target === "boolean") {
            deep = target;

            // skip the boolean and the target
            target = arguments[i] || {};
            i++;
        }

        // Handle case when target is a string or something (possible in deep copy)
        if (typeof target !== "object" && !jQuery.isFunction(target)) {
            target = {};
        }

        // extend jQuery itself if only one argument is passed
        if (i === length) {
            target = this;
            i--;
        }

        for (; i < length; i++) {
            // Only deal with non-null/undefined values
            if ((options = arguments[i]) != null) {
                // Extend the base object
                for (name in options) {
                    src = target[name];
                    copy = options[name];

                    // Prevent never-ending loop
                    if (target === copy) {
                        continue;
                    }

                    // Recurse if we're merging plain objects or arrays
                    if (deep && copy && (jQuery.isPlainObject(copy) || (copyIsArray = jQuery.isArray(copy)))) {
                        if (copyIsArray) {
                            copyIsArray = false;
                            clone = src && jQuery.isArray(src) ? src : [];

                        } else {
                            clone = src && jQuery.isPlainObject(src) ? src : {};
                        }

                        // Never move original objects, clone them
                        target[name] = jQuery.extend(deep, clone, copy);

                        // Don't bring in undefined values
                    } else if (copy !== undefined) {
                        target[name] = copy;
                    }
                }
            }
        }

        // Return the modified object
        return target;
    };
 

jQuery.extend() (把兩個或者更多的物件合併到第一個當中)。擴充套件也就是所謂的靜態方法,只跟這個 類 本身有關。跟你具體的例項化物件是沒關係的。

jQuery.fn.extend() (把物件掛載到jQuery的prototype屬性，來擴充套件一個新的jQuery例項方法)

jQuery.fn = jQuery.prototype = {
      init:funtion(selector,context){
            //..... 
 
     }
}

jQuery.fn.extend拓展的是jQuery物件（原型的）的方法，物件是啥？就是類的例項化嘛，例如$("#abc") ，$(div)。jQuery.fn.extend拓展的方法，你得用在jQuery物件上面才行

 // Initialize a jQuery object


    // A central reference to the root jQuery(document)
    var rootjQuery,

        // Use the correct document accordingly with window argument (sandbox)
        document = window.document,

        // A simple way to check for HTML strings
        // Prioritize #id over <tag> to avoid XSS via location.hash (#9521)
        // Strict HTML recognition (#11290: must start with <)
        rquickExpr = /^(?:\s*(<[\w\W]+>)[^>]*|#([\w-]*))$/,

        init = jQuery.fn.init = function (selector, context) {
            var match, elem;

            // HANDLE: $(""), $(null), $(undefined), $(false)
            if (!selector) {
                return this;
            }

            // Handle HTML strings
            if (typeof selector === "string") {
                if (selector.charAt(0) === "<" && selector.charAt(selector.length - 1) === ">" && selector.length >= 3) {
                    // Assume that strings that start and end with <> are HTML and skip the regex check
                    match = [null, selector, null];

                } else {
                    match = rquickExpr.exec(selector);
                }

                // Match html or make sure no context is specified for #id
                if (match && (match[1] || !context)) {

                    // HANDLE: $(html) -> $(array)
                    if (match[1]) {
                        context = context instanceof jQuery ? context[0] : context;

                        // scripts is true for back-compat
                        // Intentionally let the error be thrown if parseHTML is not present
                        jQuery.merge(this, jQuery.parseHTML(
                            match[1],
                            context && context.nodeType ? context.ownerDocument || context : document,
                            true
                        ));

                        // HANDLE: $(html, props)
                        if (rsingleTag.test(match[1]) && jQuery.isPlainObject(context)) {
                            for (match in context) {
                                // Properties of context are called as methods if possible
                                if (jQuery.isFunction(this[match])) {
                                    this[match](context[match]);

                                    // ...and otherwise set as attributes
                                } else {
                                    this.attr(match, context[match]);
                                }
                            }
                        }

                        return this;

                        // HANDLE: $(#id)
                    } else {
                        elem = document.getElementById(match[2]);

                        // Check parentNode to catch when Blackberry 4.6 returns
                        // nodes that are no longer in the document #6963
                        if (elem && elem.parentNode) {
                            // Handle the case where IE and Opera return items
                            // by name instead of ID
                            if (elem.id !== match[2]) {
                                return rootjQuery.find(selector);
                            }

                            // Otherwise, we inject the element directly into the jQuery object
                            this.length = 1;
                            this[0] = elem;
                        }

                        this.context = document;
                        this.selector = selector;
                        return this;
                    }

                    // HANDLE: $(expr, $(...))
                } else if (!context || context.jquery) {
                    return (context || rootjQuery).find(selector);

                    // HANDLE: $(expr, context)
                    // (which is just equivalent to: $(context).find(expr)
                } else {
                    return this.constructor(context).find(selector);
                }

                // HANDLE: $(DOMElement)
            } else if (selector.nodeType) {
                this.context = this[0] = selector;
                this.length = 1;
                return this;

                // HANDLE: $(function)
                // Shortcut for document ready
            } else if (jQuery.isFunction(selector)) {
                return typeof rootjQuery.ready !== "undefined" ?
                    rootjQuery.ready(selector) :
                    // Execute immediately if ready is not present
                    selector(jQuery);
            }

            if (selector.selector !== undefined) {
                this.selector = selector.selector;
                this.context = selector.context;
            }

            return jQuery.makeArray(selector, this);
        };

    // Give the init function the jQuery prototype for later instantiation
    init.prototype = jQuery.fn;

    // Initialize central reference
    rootjQuery = jQuery(document);

js中國每個函式都會有一個Arguments物件例項arguments，它引用著函式的實參，arguments.length為函式實參個數，arguments.callee引用函式自身。

在js中 不需要明確指出引數名，就能訪問它們

function test() {
        var s = "";
        for (var i = 0; i < arguments.length; i++) {
            alert(arguments[i]);
            s += arguments[i] + ",";
        }
        return s;
    }
    test("name", "age")

輸出結果：

name,age

arguments本身並不是陣列而是物件，它只在函式內部起作用，並且永遠指向當前函式的呼叫者傳入的所有引數，函式的實參集合，這裡的實參是重點，就是執行函式時實際傳入的引數的集合。arguments類似Array但它不是一個Array

arguments有length屬性，可以用arguments[length]顯示呼叫

[].slice.call(arguments)或者Array.prototype.slice.call(arguments)，就是擷取（更重要的是獲取，slice是得到子陣列）函式的引數，然後讓arguments等“偽陣列”也可以使用陣列的各種方法。

    var deletedIds = [];

    var slice = deletedIds.slice;
	
	    var
        version = "1.11.3",

        // Define a local copy of jQuery
        jQuery = function (selector, context) {
            // The jQuery object is actually just the init constructor 'enhanced'
            // Need init if jQuery is called (just allow error to be thrown if not included)
            return new jQuery.fn.init(selector, context);
        }
		
	 jQuery.fn = jQuery.prototype = {
        // The current version of jQuery being used
        jquery: version,

        constructor: jQuery,

        // Start with an empty selector
        selector: "",

        // The default length of a jQuery object is 0
        length: 0,
	
	slice: function () {
            return this.pushStack(slice.apply(this, arguments));
    }
	    // For internal use only.
        // Behaves like an Array's method, not like a jQuery method.
        push: push,
        sort: deletedIds.sort,
        splice: deletedIds.splice
    };

callee屬性，返回正被執行的Function 物件，也就是所指定的 Function 物件的正文。callee 屬性是 arguments 物件的一個成員，僅當相關函式正在執行時才可用。
callee 屬性的初始值就是正被執行的 Function 物件，這允許匿名的遞迴函式。

var sum = function (n) {
        if (1 == n) {
            return 1;
        } else {
            return n + arguments.callee(n - 1);
        }
    }
    alert(sum(6));

通俗一點就是，arguments此物件大多用來針對同個方法多處呼叫並且傳遞引數個數不一樣時進行使用。根據arguments的索引來判斷執行的方法。