In Postman, we often need to monitor the outcomes of our requests, particularly to catch failures and understand why they happened. Using JavaScript within Postman’s scripting capabilities, we can create a script to log failed requests in a structured format. Below, we will walk through the steps to set this up.

Step 1: Understand the Basics

Postman has two scripting sections: Pre-request Script and Tests. The Tests section runs after the request completes and is the ideal place for logging the results of API calls.

Step 2: Writing the Script

1. Open Postman and select your request.
2. Navigate to the "Tests" tab.

Here’s a simple script that logs failed requests with relevant details such as the request URL, HTTP method, response code, and error message.

pm.test("Log failed requests", function() {
    if (pm.response.code >= 400) { // Check if the response code indicates a failure
        // Create an object to hold the log details
        const logDetails = {
            timestamp: new Date().toISOString(),
            url: pm.request.url.toString(),
            method: pm.request.method,
            status: pm.response.code,
            errorMessage: pm.response.status,
            responseBody: pm.response.text() // Capture the response body for additional context
        };

        // Convert the log details to a string and log it to the console
        console.error(JSON.stringify(logDetails, null, 2));
        
        // Optionally, save the log to an environment variable for persistence
        if (!pm.environment.get("failedRequests")) { 
            pm.environment.set("failedRequests", JSON.stringify([]));
        }
        const currentLogs = JSON.parse(pm.environment.get("failedRequests"));
        currentLogs.push(logDetails);
        pm.environment.set("failedRequests", JSON.stringify(currentLogs));
    }
});

Step 3: Explained Breakdown

• pm.test(): This function is used to define a test case. Within it, we check for conditions and log failures.
• pm.response.code: The HTTP response code is checked. If it’s 400 or higher, it’s considered a failure.
• Log Details Object:
  • timestamp: Using new Date().toISOString() captures the exact time when the failure occurred.
  • url: The request URL is captured using pm.request.url.toString().
  • method: This captures the request method (GET, POST, etc.).
  • status: The HTTP response code is stored here.
  • errorMessage: Provides a short description of the error.
  • responseBody: Captures the response body, which may provide more context on the error condition.
• Logging: Using console.error(), we output the log details to the console, making it easy to track failed requests.
• Environment Variables: We store the logs in an environment variable called “failedRequests”. This allows you to persist the logs across different requests or sessions.

Step 4: Testing Your Script

To test the script:

1. Trigger a request that you expect to fail (for example, a non-existing endpoint).
2. Check the Console in Postman (found at the bottom of the app or via View -> Show Postman Console).
3. You should see the formatted log entries when the request fails.

By implementing this script, you will improve your ability to monitor and troubleshoot issues in your API requests efficiently.