Examples of jquery's each method

The each () function is a tool-class function provided by almost all frameworks. Through it, You can traverse and process the attribute values of objects and arrays, jQuery and jQuery objects both implement this method. The following describes how to use this method for jQuery objects, but simply delegates the each method: the jQuery object is passed to jQuery's each method as the first parameter. in other words, the each method provided by jQuery calls all the child elements of the object provided by parameter 1 one by one. The each method provided by the jQuery object calls the child elements in jQuery one by one.

The Code is as follows:

JQuery. prototype. each = function (fn, args ){
Return jQuery. each (this, fn, args );
}

Let's take a look at the specific implementation of the each method provided by jQuery, jQuery. each (obj, fn, arg)

This method has three parameters: the object for the operation (obj), the fn function for the operation, and The args parameter of the function.

Let's discuss it based on the ojb object:

1. The obj object is an array.

The each method calls the fn function one by one for the sub-elements of the array until the returned result of a sub-element is false. That is to say, we can process the fn function provided, the each method is called after certain conditions are met. When the each method provides the arg parameter, the incoming parameter of the fn function call is arg. Otherwise, it is a sub-element index and the sub-element itself.

2. The obj object is not an array.

The biggest difference between this method and 1 is that the fn method will be carried out without considering the return value. In other words, all properties of the obj object are called by the fn method, even if the fn function returns false. The input parameters of the call are similar to those of 1.

The Code is as follows:

JQuery. each = function (obj, fn, args ){
If (args ){
If (obj. length = undefined ){
For (var I in obj)
Fn. apply (obj, args );
} Else {
For (var I = 0, ol = obj. length; I <ol; I ++ ){
If (fn. apply (obj, args) = false)
Break;
}
}
} Else {
If (obj. length = undefined ){
For (var I in obj)
Fn. call (obj, I, obj );
} Else {
For (var I = 0, ol = obj. length, val = obj [0]; I <ol & fn. call (val, I, val )! = False; val = obj [++ I]) {}
}
}
Return obj;
}

Note that the call method of fn in the each method does not use simple fn (I, val) or fn (args), but uses fn. call (val, I, val) or fn. apply (obj. args), which means that in your own fn implementation, you can directly use the this pointer to reference arrays or child elements of objects. This is an implementation method adopted by the vast majority of jQuery.