var obj = document.getElementById('container'),
jq = $(obj);

console.log(jq.length); //1
console.log(jq.context); //obj
console.log(jq.[0]); //obj

var jqHTML = $('<h1>文章標題</h1><p>內容</p>');
console.log(jqHTML); //[<h1>,<p>];

var jqHTML = $('<div></div>', { class: 'css-class', data-name: 'data-val' });

console.log(jqHTML.attr['class']); //css-class
console.log(jqHTML.attr['data-name']); //data-val

var jq = $('#container');

console.log(jq.[0]); //包含的dom節點元素
console.log(jq.length); //1
console.log(jq.context); //document
console.log(jq.selector); //container

return jQuery(document).find(className);

return jQuery(context).find(className);

<div class="main">
<h2 class="title">主內容標題</h2>
<p>主標題</p>
</div>
<div class="sub">
<h2 class="title">次內容標題</h2>
<p>次標題</p>
</div>

var jq, context;
context = '.sub';
var jq = $('.title', context);
console.log(jq.text()); //次內容標題
console.log(jq.context); //document
console.log(jq.selector); //.sub .title
context = $('.sub');
var jq = $('.title', context);
console.log(jq.text()); //次內容標題
console.log(jq.context); //document
console.log(jq.selector); //.sub .title
context = $('.sub')[0];
var jq = $('.title', context);
console.log(jq.text()); //次內容標題
console.log(jq.context); //className為sub的節點元素
console.log(jq.selector); //.title

$(function(e){
console.log('DOMContent is loaded');
})
//上面代碼等同于：
jQuery(document).ready(function(e) {
console.log('DOMContent is loaded');
});

var jq = $('#container');
console.log(jq.selector); // #container
console.log(jq.context); // document

var jq2 = $($('#container'));
console.log(jq2.selector); // #container
console.log(jq2.context); // document

var rootjQuery = $(document),
rquickExpr = /^(?:[^#<]*(<[/w/W]+>)[^>]*$|#([/w/-]*)$)/;
jQuery.fn = jQuery.prototype = {
init: function( selector, context, rootjQuery ) {
var match, elem, ret, doc;
// Handle $(""), $(null), $(undefined), $(false)
if ( !selector ) {
return this;
}
// Handle $(DOMElement)
if ( selector.nodeType ) {
this.context = this[0] = selector;
this.length = 1;
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
// match[1]不為null，則為html字符串，match[2]不為null，則為元素id
if ( match && (match[1] || !context) ) {
// HANDLE: $(html) -> $(array)
if ( match[1] ) {
context = context instanceof jQuery ? context[0] : context;
doc = ( context && context.nodeType ? context.ownerDocument || context : document );
// scripts is true for back-compat
// selector是由文檔碎片中的childnodes組成的數組
selector = jQuery.parseHTML( match[1], doc, true );
// 如果match[1]為空的單標簽元素(如：<div><div>)且context為對象字面量
if ( rsingleTag.test( match[1] ) && jQuery.isPlainObject( context ) ) {
// 如果context對象不為空，則將對象中的屬性添加到selector數組中僅有的dom節點中
this.attr.call( selector, context, true );
}
// merge函數的參數應該為兩個數組，目的是將第二個數組中的項合并到第一個數組，而this并不是一個數組，
// this是選擇器init構造函數的實例對象，該對象繼承jQuery.prototype對象中的length屬性(默認為0)，因此可以理解好merge函數源碼
// 將selector中的dom項合并到this對象中，并返回該對象
return jQuery.merge( this, selector );
// 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
// ie6，7和Opera存在此bug，當一個標簽name和一個標簽id值相等時，
// document.getElementById(#id)函數將返回提前出現的標簽元素
if ( elem.id !== match[2] ) {
// 如果存在以上Bug，則返回由find函數返回的document文檔的后代元素集合
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, $(...))
// context不存在或者context為jQuery對象
} else if ( !context || context.jquery ) {
return ( context || rootjQuery ).find( selector );
// HANDLE: $(expr, context)
// (which is just equivalent to: $(context).find(expr)
// context為className或者dom節點元素
} else {
// 等同于jQuery(context).find(selector)
return this.constructor( context ).find( selector );
}
// 處理$(fn)===$(document).ready(fn)
} else if ( jQuery.isFunction( selector ) ) {
return rootjQuery.ready( selector );
}
// 處理$(jQuery對象)
if ( selector.selector !== undefined ) {
this.selector = selector.selector;
this.context = selector.context;
}
// 當第一個參數selector為jQuery對象時，將selector中的dom節點合并到this對象中，并返回this對象
return jQuery.makeArray( selector, this );
}
}