Develop javascript error reporting tool

Preface

In front-end development, error reporting is a common and important issue. When a user encounters an error, we need to collect the error information and report it to the server or third-party platform. If there are no error reports, we will not be able to locate the problem and make timely repairs.

This article will explain how to develop a JavaScript-based error reporting tool so that we can quickly discover and solve problems during the development process.

Step One: Collecting Error Information

There are usually two types of front-end errors: JavaScript errors and resource errors. JavaScript errors usually refer to syntax errors or runtime errors. Resource errors include loading failure, network request failure, etc.

1. JavaScript error collection

To collect JavaScript errors, we need to bind the error event on the window object and collect error information. The error event usually has three attributes: message, filename and lineno:

window.onerror = function(message, source, lineno, colno, error) {
  console.log('Error:', message, source, lineno, colno, error);
  // 上报错误信息
}

This event will be triggered when JavaScript on a page throws an uncaught exception. In this event handler, we can print information about the error message to the console and report it to the server or third-party platform.

2. Collection of resource errors

To collect resource errors, we need to bind the error event on the window object and collect resource information. Usually, when a resource error occurs, we will receive a load failed event. This event can be captured by binding the error event on the window object:

window.addEventListener('error', function(event) {
  var target = event.target || event.srcElement;
  console.log('Load error:', target.tagName, target.src, event.message);
  // 上报错误信息
}, true);

This event handler will be triggered when any resource in the page fails to load. In this event handler, we can print error information to the console and report it to the server or third-party platform.

Step Two: Reporting Error Information

When we collect error information, the next step is to report it to the server or third-party platform. We can achieve this through Ajax requests, Image objects, or using third-party libraries. In this article, we will use the method of submitting Ajax requests to achieve this.

1. Ajax request reporting

Assuming we are using the jQuery library, we can use the following code to send a reporting request to the server:

$.ajax({
  url: '/api/report-error',
  method: 'POST',
  data: {
    message: message,
    source: source,
    lineno: lineno,
    colno: colno,
    error: error && error.stack
  }
});

Pass By sending a POST request, we can send the error message to the server in the form of data. In the background, we can obtain this information by parsing the request body to locate and repair errors.

2. Image object reporting

If we don’t want to use Ajax requests or jQuery libraries, we can use the Image object to send a GET request to the server:

var img = new Image();
img.src = '/api/report-error?message=' + encodeURIComponent(message)
  + '&source=' + encodeURIComponent(source)
  + '&lineno=' + encodeURIComponent(lineno)
  + '&colno=' + encodeURIComponent(colno)
  + '&error=' + encodeURIComponent(error && error.stack);

The disadvantage of this method is that we need to splice the error information into the query string, which may cause the URL to be too long.

3. Third-party library reporting

In addition to developing error reporting tools ourselves, we can also use some third-party libraries to complete this task. Among them, some of the more popular error reporting libraries include:

• Sentry: an open source error reporting service that provides error grouping, Web interface, API and SDK functions;
• Bugsnag: A real-time error monitoring and reporting tool that automatically detects errors and provides various functions such as error tracking, error analysis, etc.;
• New Relic: an application performance monitoring tool that provides real-time error reporting and analysis and positioning errors.

The usage methods of these libraries are similar. We only need to configure them according to their documentation guidelines.

Step Three: Performance Optimization

After we complete the development of the error reporting tool, we need to perform some performance optimization to ensure that the tool has less impact on the performance of the website.

1. Merge error information

If there are multiple JavaScript scripts on the page, when an error occurs in a script, we need to report the error information to the server. If we bind the error event in every script, then we will send multiple requests. In order to reduce the number of requests, we can combine multiple error messages into one request and use Buffer for caching.

2. Sampling reporting

When the page traffic is large, the amount of data reported incorrectly may be very large. In order to avoid excessive burden on the server, we can introduce a sampling reporting mechanism and only report a part of the error information. For example, we can set an error reporting rate, and only send error information to the server in proportion to the error reporting rate.

3. Reporting based on network environment

In a low-speed network environment, error reporting will have a great impact on performance and may even cause the page to crash. In order to avoid this situation from happening, we can automatically adjust the error reporting rate based on the current network environment conditions. For example, we can set the error reporting rate to 100% (that is, report all) under 4G, and reduce the rate to 20% under 2G.

Conclusion

Developing JavaScript error reporting tools is very important for front-end developers. It can help us quickly locate and solve problems and improve user experience. In this article, we explain aspects such as collecting error information, reporting error information, and performance optimization. Hope this article helps you!

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