Access server error javascript

JavaScript, which is widely used in Web development, is an object- and event-driven scripting language. It can not only be used for front-end interaction and interface design, but also can communicate with the server through ajax technology. Although JavaScript is widely used in web development, some errors and problems are often encountered when accessing the server. This article will introduce some JavaScript errors that may occur when accessing the server and give corresponding solutions.

Error 1: Cross-domain access

Because the web browser has a Same-origin policy, JavaScript cannot access data under other domain names. The same-origin policy means that JavaScript can only access resources in the same protocol, domain name, and port as the current web page. For example, the data of http://www.example2.com cannot be accessed from http://www.example1.com through JavaScript. This is because cross-domain access may cause security issues, such as malicious websites using cross-domain methods to obtain user private data.

Solution: Use JSONP technology or CORS (Cross-origin resource sharing).

JSONP can use the src attribute of the tag to make cross-domain requests, because the tag is not restricted by the same-origin policy and can package the response data into a JavaScript function and return it to the page. . CORS achieves cross-domain access by setting the Access-Control-Allow-Origin header on the server side.

Error 2: Asynchronous access

Since JavaScript is a single-threaded execution language, and HTTP requests are asynchronous, this will cause the execution time of the callback function to be uncontrollable when accessing the server. In other words, the timing of response data return is uncertain. If the callback function of an asynchronous request does not process the response data in time, an access server error will occur.

Solution: Use callback function or Promise.

By registering a callback function when initiating a request, the data can be processed in time when the response data returns. One disadvantage of callback functions is that callbacks are prone to nesting, making the code difficult to understand and maintain. In order to solve this problem, ES6 introduced Promise, which can handle asynchronous requests more conveniently and can be called in chains, making the code more elegant.

Error 3: Server problem

When JavaScript accesses the server, some unpredictable and avoidable problems may occur, such as network delays, DNS resolution errors, server access errors, etc. These issues have the potential to disrupt the stability and performance of the entire web application.

Solution: Use try catch statement, set timeout and other means.

When accessing the server, you can use the try catch statement to catch exceptions to ensure the robustness of the code. In addition, you can also set a timeout. If the request time exceeds the limit, the request will be interrupted and an error message will be returned. This prevents web applications from crashing due to long server response times.

Error 4: Security Issues

When JavaScript accesses the server, it may be attacked due to security issues, such as XSS (Cross-site scripting) attacks, CSRF (Cross-site request forgery) Attack etc. These attacks have the potential to tamper with or steal user data and are difficult to detect and prevent.

Solution: Use CSRF tokens, verify input data, etc.

For CSRF attacks, you can use the CSRF token to prevent it. The CSRF token is a randomly generated string. The server will place it in the form, cookie, etc. in the Web page. If the client requests If the correct CSRF token is carried, the server will verify it, otherwise it will reject the request. For XSS attacks, you can prevent malicious scripts from being inserted into the page by validating the data entered on the front end.

Conclusion

In web development, JavaScript communicating with the server is very common, but there are also many problems and errors. This article introduces some common errors and corresponding solutions. These solutions can help us avoid some common access server errors and ensure the stability and performance of web applications.