插件編寫---jquery源碼品讀之入口extend（1）

//整個extend函數表明着如何尋找過來的參數（能夠是任何對象【數組也是對象】），返回須要的對象。在javascirpt中extend理論之一是合併或複製對象。那麼如何<pre name="code" class="javascript">複製<span style="font-family: Arial, Helvetica, sans-serif;">呢？基本的理論在個人http://blog.csdn.net/luozhonghua2014/article/details/45790867文章中。jquery源碼真實體現了這些理論。讀者朋友研究源碼，建議除了基本理論外，建議寫個插件或直接用jquery的方法去debugger;這樣很容易看到jquery如何工做及優勢。編寫優於jquery的插件或補充是程序員的前端基本功，也是走向高級架構師的入點。</span>

jQuery.extend = jQuery.fn.extend = function() {
	var options, name, src, copy, copyIsArray, clone,
		target = arguments[0] || {},
		i = 1,
		length = arguments.length,
		deep = false;

	// Handle a deep copy situation
	if ( typeof target === "boolean" ) {
		deep = target;
		target = arguments[1] || {};
		// skip the boolean and the target
		i = 2;
	}

	// 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 ( length === i ) {
		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;
};