看了一下午还是有很多地方没弄明白，jQuery的一些工具方法的原理也不完全清楚，这篇文章会随着我深入阅读jQuery源码的同时不断更新。
// Initialize a jQuery object
// 初始化Jquery对象 // 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 <)
// 检测html字符串的正则表达式
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
// 下面的match中，match[0]存放原字符串，match[1]存html标签，match[2]存#q中的“q”
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
//selector是HTML标签，类似<div>123</div>
match = [ null, selector, null ]; } else {
//不是html标签
match = rquickExpr.exec( selector );
} // Match html or make sure no context is specified for #id
// 匹配的html或确保没有上下文指定为# id
if ( match && (match[1] || !context) ) { // HANDLE: $(html) -> $(array)
// 1.处理html标签
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( first, second ) 合并两个数组内容到第一个数组
//jQuery.parseHTML()函数用于将HTML字符串解析为对应的DOM节点数组
//对于HTML文档来说，documentElement是<html>标签对应的Element对象，ownerDocument是document对象
jQuery.merge( this, jQuery.parseHTML(
match[1],
context && context.nodeType ? context.ownerDocument || context : document,
true
) ); // HANDLE: $(html, props)
// rsingleTag匹配匹配独立标签，比如'<html></html>'或者'<div></div>'
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)
//2.处理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, $(...))
//3.处理表达式
} else if ( !context || context.jquery ) {
return ( context || rootjQuery ).find( selector ); // HANDLE: $(expr, context)
// (which is just equivalent to: $(context).find(expr)
//4.处理有上下文的表达式
} else {
return this.constructor( context ).find( selector );
} // HANDLE: $(DOMElement)
//5.处理DOM元素
} else if ( selector.nodeType ) {
this.context = this[0] = selector;
this.length = 1;
return this; // HANDLE: $(function)
// Shortcut for document ready
//6.处理函数
} 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 );
};