jQuery源码 ―each步骤

each: function( object, callback, args ) {
	var name, i = 0,
		length = object.length,
		// 这样判断是否为Object还挺奇怪的，下面的代码根据{key:value}和[]两种类型进行遍历
		// 一般来说，Element和{}对象的length属性是undefined
		isObj = length === undefined || jQuery.isFunction( object );
	
	if ( args ) {
		if ( isObj ) {
			for ( name in object ) {
				if ( callback.apply( object[ name ], args ) === false ) {
					break;
				}
			}
		} else {
			for ( ; i < length; ) {
				if ( callback.apply( object[ i++ ], args ) === false ) {
					break;
				}
			}
		}
	
	// A special, fast, case for the most common use of each
	} else {
		if ( isObj ) {
			for ( name in object ) {
				// 如果回调函数return false;就中断遍历
				if ( callback.call( object[ name ], name, object[ name ] ) === false ) {
					break;
				}
			}
		} else {
			for ( ; i < length; ) {
				if ( callback.call( object[ i ], i, object[ i++ ] ) === false ) {
					break;
				}
			}
		}
	}
	
	return object;
}

/**
 * args有无值，回调函数的参数不同
 * args有值时：(当前项，args)
 * args无值时：(object，name, 当前值)
 *
 */
function each( object, callback, args ) {
	var name; //遍历时引用对象的key
	if( args ){
		for( name in object ) {
			if( object.hasOwnProperty( name )) {
				if( callback.apply( object[name], args ) === false ) {
					break;
				}
			}
		}
	} else {
		for( name in object ) {
			if( object.hasOwnProperty( name )) {
				if( callback.call( object, name, object[name]) === false ) {
					break;
				}
			}
		}
	}
	// 返回处理后的object
	return object;
}