(92-176)

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 );
    },

    map: function( callback ) {
        return this.pushStack( jQuery.map(this, function( elem, i ) {
            return callback.call( elem, i, elem );
        }));
    },

    slice: function() {
        return this.pushStack( slice.apply( this, arguments ) );
    },

    first: function() {
        return this.eq( 0 );
    },

    last: function() {
        return this.eq( -1 );
    },

    eq: function( i ) {
        var len = this.length,
            j = +i + ( i < 0 ? len : 0 );
        return this.pushStack( j >= 0 && j < len ? [ this[j] ] : [] );
    },

    end: function() {
        return this.prevObject || this.constructor(null);
    },

    // For internal use only.
    // Behaves like an Array‘s method, not like a jQuery method.
    push: push,
    sort: arr.sort,
    splice: arr.splice
};

//模仿出一个类数组对象
var a = { 0: 2, 1: 4, 2: 6,length:3}
console.log(Array.prototype.slice.call(a));//[ 2, 4, 6 ]

var arr = [],
slice = arr.slice;
//提取出get，这个操作会覆盖原代码中的get    
jQuery.fn.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 );
}
var $div = $(‘div‘)
//正数和0
//这个情况下与[]访问符效果一样
console.log($div.get(0) === $div[0])

//负数位置
console.log($div.get(-1))

//为空时转化为将对象数组，
console.log($div.get())

if( a != null ){
    if( a<0 ){
        this[ num + this.length ]
    }else{
        this[ num ] 
    }
}else{
    slice.call( this )
}

//等价于
a != null ?( num < 0 ? this[ num + this.length ] : this[ num ] ) :slice.call( this );

var $ = {0:1,prev: Object.prototype}
console.log($[0])
$ = {0:2,prev:$}
console.log($[0])
$ = {0:3,prev:$}
console.log($[0])

//回溯
$ = $.prev
console.log($[0])

var slice = [].slice;
jQuery.fn.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;
}
jQuery.fn.slice = function() {
        return this.pushStack( slice.apply( this, arguments ) );
}
jQuery.merge = function( first, second ) {
        var len = +second.length,
            j = 0,
            i = first.length;

        for ( ; j < len; j++ ) {
            first[ i++ ] = second[ j ];
        }

        first.length = i;

        return first;
}
jQuery.fn.end = function() {
        return this.prevObject || this.constructor(null);
}
console.log($(‘li‘).slice(2,4).css(‘background-color‘,‘red‘).end());