Detailed explanation of each() method in jquery using examples

The

each() function is a tool function provided by basically all frameworks. Through it, you can traverse the attribute values ​​​​of objects and arrays and process them. Both jQuery and jQuery objects implement this method. For jQuery objects, the each method is simply delegated: the jQuery object is passed as the first parameter to jQuery's each method. In other words: the each method provided by jQuery is All sub-elements in the object provided by parameter 1 are called one by one. The each method provided by the jQuery object calls the sub-elements inside jQuery one by one.

Here are some common uses of each

1. each handles one-dimensional array

 var arr1 = [ "aaa", "bbb", "ccc" ];      
  $.each(arr1, function(i,val){      
      alert(i);   
      alert(val);
  });

alert( i) Will output 0, 1, 2
alert(val) will output aaa, bbb, ccc

2. Each handles two-dimensional array

　var arr2 = [['a', 'aa', 'aaa'], ['b', 'bb', 'bbb'], ['c', 'cc', 'ccc']]      
　　$.each(arr, function(i, item){      
      alert(i);   
      alert(item);      
　　});

arr2 For a two-dimensional array, item is equivalent to taking each array in this two-dimensional array.
item[0] is relative to taking the first value in each one-dimensional array
alert(i) will output 0, 1, 2, because this two-dimensional array contains 3 array elements
alert(item) will be output as ['a', 'aa', 'aaa'], ['b', 'bb', 'bbb'], ['c', 'cc', 'ccc']

After slightly changing the processing of this two-digit array

var arr = [['a', 'aa', 'aaa'], ['b', 'bb', 'bbb'], ['c', 'cc', 'ccc']]      
 　　$.each(arr, function(i, item){      
      　　$.each(item,function(j,val){
       　　　　 alert(j);
        　　　　alert(val);
    　}); 
});

alert(j) will output 0, 1, 2, 0, 1, 2, 0, 1 , 2

alert(val) will output as a, aa, aaa, b, bb, bbb, c, cc, ccc

each processes json data, this each has Even more powerful, you can loop through each attribute

var obj = { one:1, two:2, three:3};      
 　　each(obj, function(key, val) {      
      　　alert(key);   
      　　alert(val);      
 　　});

Here alert(key) will output one two three
alert(val) will output one, 1, two, 2, three, 3
This Why is the key not a number but an attribute? Because the json format is a set of unordered attributes and values. Since it is unordered, where are the numbers?
And this val is equivalent to obj[key]

ecah processes dom elements. Here, an input form element is used as an example.

If you have a piece of code like this in your dom
faccfcae027ff734f73dd06266eca48e
cc896bc9d5d56de012ad70ceb9db5a87
a64ed2e9863cf3d87033948a4a36efde
4fffe49a5b668cdd8d1f20439e1143d9
Then you use each as follows

$.each($("input:hidden"), function(i,val){  
     alert(val);
     alert(i);
     alert(val.name);
     alert(val.value);   
 });

Then, alert(val) will output [object HTMLInputElement] because it is a form element.

alert(i) will output 0, 1, 2, 3

alert(val.name); will output aaa, bbb, ccc, ddd, if you use this. name will output the same result
alert(val.value); will output 111,222,333,444, if this.value is used, the same result will be output

each(callback) With each match The element serves as a context to perform a function.
means that every time the function passed in is executed, the this keyword in the function points to a different DOM element (a different matching element each time). Moreover, every time the function is executed, a numeric value representing the position of the element as the execution environment in the set of matching elements is passed to the function as a parameter (an integer starting from zero). Returning 'false' will stop the loop (just like using 'break' in a normal loop). Return 'true' to jump to the next loop (just like using 'continue' in a normal loop).
The following callback is the callback function, which indicates the operation that should be given when traversing the elements. Let’s look at a simple example below:
Iterate over two images and set their src attributes. Note: here this refers to the DOM object rather than the jQuery object.

each() method specifies a function to run for each matching element.
Tip: Returning false can be used to stop the loop early.
Syntax
$(selector).each(function(index,element)) Parameter Description
function(index,element) Required. Specifies the function to run for each matching element.
•index - the index position of the selector
•element - the current element (the "this" selector can also be used)

$("button").click(function(){ 
$("li").each(function(){ 
alert($(this).text()) 
}); 
});

那怎么跳出each呢 
jquery再遍历选定的对象时候用each比较方便。有种应用是找到里面符合条件的对象后，要跳出这个循环。
javascript的跳出循环一般用break. 
同事遇到这个问题，下意识 的用了break，想跳出这个循环。结果报错 
SyntaxError: unlabeled break must be inside loop or switch 
经查，应该用一个 在回调函数里return false即可，大多数jq的方法都是如此的 

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