Shulou(Shulou.com)06/03 Report--

This article mainly introduces "how to deal with variable conflicts". In daily operation, I believe many people have doubts about how to deal with variable conflicts. The editor consulted all kinds of data and sorted out simple and easy-to-use methods of operation. I hope it will be helpful for you to answer the doubts about "how to deal with variable conflicts"! Next, please follow the editor to study!

The code to create the XMLHttpRequest object for the book is as follows:

Var xmlHttp

Function createXMLHttpRequest () {if (window.ActiveXObject) {xmlHttp = new ActiveXObject ("Microsoft.XMLHTTP");} else if (window.XMLHttpRequest) {xmlHttp = new XMLHttpRequest ();}}

In general, the use of this code does not cause any problems.

Such as:

Function test1 () {createXMLHttpRequest (); xmlHttp.onreadystatechange = handleStateChange1; url = "test.php?ts=" + new Date (). GetTime (); xmlHttp.open ("GET", url, true); xmlHttp.send (null);}

Function test2 () {createXMLHttpRequest (); xmlHttp.onreadystatechange = handleStateChange2; url = "test.php?ts=" + new Date (). GetTime (); xmlHttp.open ("GET", url, true); xmlHttp.send (null);}

Function handleStateChange1 () {.

}

Function handleStateChange2 () {.

}

.

Calling the test1,test2 function from different parts of the page works fine. That is, if it is called at different times, there will be no problem.

But if you need to call both functions at the same time, you will find that only one of them works properly.

For example, when I load the page, I run the following function:

Function init () {test1 (); test2 ();}

At this point, only one function in test1,test2 will execute normally.

According to the analysis, it is due to the language characteristics of javascript. In general, Javascript variables, functions, and so on, are common, and other objects can be accessed (readable and writable). That's the problem. At the same time, there is a conflict of "variable xmlHttp" when calling test1 and test2.

Solution:

1 the simplest method, do not call at the same time, for example, the init function can be changed to:

Function init () {test1 (); setTimeout ("test2 ()");}

However, this method belongs to speculation and does not really solve the problem.

2 modify the "XMLHttpRequest creation function" to an instantiated function.

Function createXMLHttpRequest () {if (window.ActiveXObject) {var xmlHttpObj = new ActiveXObject ("Microsoft.XMLHTTP");} else if (window.XMLHttpRequest) {var xmlHttpObj = new XMLHttpRequest ();} return xmlHttpObj;}

When instantiated, change it to:

Function test1 () {xmlHttp_1 = createXMLHttpRequest ()

XmlHttp_1.onreadystatechange = handleStateChange1; url_1 = "test.php?ts=" + new Date (). GetTime (); xmlHttp_1.open ("GET", url, true); xmlHttp_1.send (null);}

Function test2 () {xmlHttp_2 = createXMLHttpRequest ()

XmlHttp_2.onreadystatechange = handleStateChange1; url_2 = "test.php?ts=" + new Date (). GetTime (); xmlHttp_2.open ("GET", url, true); xmlHttp_2.send (null);}

In this way, even if the test1,test2 function is called at the same time, there will be no problem, and real "synchronization" will be achieved.

# # #

With this method, you can derive the method for creating "private properties" of objects in javascript:

Private properties can be defined using the var keyword in the constructor.

2 Private properties can only be accessed publicly by privileged functions. A privileged function is a function defined using the this keyword in the constructor. The external client can access the privileged function, and the privileged function can access the private properties of the object.

For example, in the following Vehicle class, wheelCount and curbWeightInPounds are private properties that can only be accessed / set through privileged functions:

Function Vehicle () {var wheelCount = 4; var curbWeightInPounds = 4000

This.getWheelCount = function () {return wheelCount;}

This.setWheelCount = function (count) {wheelCount = count;}

This.getCurbWeightInPounds = function () {return curbWeightInPounds;}

This.setCurbWeightInPounds = function (weight) {curbWeightInPounds = weight;}

}

At this point, the study on "how to deal with variable conflicts" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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