jQuery中$().each与$.each的区别

在jQuery中 $().each与$.each是不同的，$().each用于对jQuery对象做遍历操作处理，而$.each用于循环遍历一个Array或Object对象，相当于for或while循环写法。

.each( function )

Description: Iterate over a jQuery object, executing a function for each matched element.

.each( function )

• function
  Type: Function( Integer index, Element element )
  A function to execute for each matched element.

The .each() method is designed to make DOM looping constructs concise and less error-prone. When called it iterates over the DOM elements that are part of the jQuery object. Each time the callback runs, it is passed the current loop iteration, beginning from 0. More importantly, the callback is fired in the context of the current DOM element, so the keyword this refers to the element.

<ul>
  <li>foo</li>
  <li>bar</li>
</ul>

$( "li" ).each(function( index ) {
  console.log( index + ": " + $( this ).text() );
});

jQuery.each( array, callback )

Description: A generic iterator function, which can be used to seamlessly iterate over both objects and arrays. Arrays and array-like objects with a length property (such as a function's arguments object) are iterated by numeric index, from 0 to length-1. Other objects are iterated via their named properties.

• jQuery.each( array, callback )

  • array
    Type: Array
    The array to iterate over.
  • callback
    Type: Function( Integer indexInArray, Object value )
    The function that will be executed on every object.

• jQuery.each( object, callback )

• object
  Type: Object
  The object to iterate over.
• callback
  Type: Function( String propertyName, Object valueOfProperty )
  The function that will be executed on every object.

The $.each() function is not the same as $(selector).each(), which is used to iterate, exclusively, over a jQuery object. The $.each() function can be used to iterate over any collection, whether it is an object or an array. In the case of an array, the callback is passed an array index and a corresponding array value each time. (The value can also be accessed through the this keyword, but Javascript will always wrap the this value as an Object even if it is a simple string or number value.) The method returns its first argument, the object that was iterated.

$.each([ 52, 97 ], function( index, value ) {
  alert( index + ": " + value );
});

var obj = {
  "flammable": "inflammable",
  "duh": "no duh"
};
$.each( obj, function( key, value ) {
  alert( key + ": " + value );
});