无法读取对象值及函数异常状态码捕获失败问题咨询

I’ve run into both of these issues myself, so let’s walk through fixes step by step!

1. Fixing the "Can't read the value of an object" Error #

This error almost always pops up for one of two reasons:

• The object you’re trying to access is null or undefined
• You’re trying to access a nested property (like obj.user.email) where an upper-level property (e.g., obj.user) doesn’t exist

Example of the Problem #

const user = getSomeUser(); // Imagine this returns null
console.log(user.email); // Boom! "Can't read property 'email' of null"

Quick Fixes #

• Use the optional chain operator (?.) (ES2020+) – this safely stops accessing properties if any step is null/undefined:

  console.log(user?.email); // Returns undefined instead of throwing an error
  

• Add explicit existence checks if you need to support older environments:

  if (user && user.email) {
    console.log(user.email);
  }
  

• Combine with nullish coalescing (??) to set a fallback value:

  const userEmail = user?.email ?? "no-email@example.com";
  

2. Correctly Capturing Error Status Codes #

The issue here is that not all error objects have a statusCode property. That property is typically only attached to HTTP-specific errors (like those from Node.js’s http module or libraries like Axios). If your error is a generic Error instance or a TypeError, err.statusCode will be undefined – which is why your code keeps hitting the else branch.

Let’s break down solutions based on your use case:

Case 1: Using Node.js’s Built-in HTTP/HTTPS Module #

For native HTTP requests, the status code lives on the response object, not the error object (errors here are usually network issues like failed connections):

const http = require('http');

http.get('https://example.com/invalid-endpoint', (res) => {
  if (res.statusCode >= 400) {
    console.log(`Error status code: ${res.statusCode}`);
  } else {
    // Handle successful response
  }
}).on('error', (err) => {
  // This is for network errors (no status code here)
  console.log('Network error:', err.message);
});

Case 2: Using an HTTP Client Like Axios #

Axios wraps HTTP errors in an object where the status code lives under err.response.status:

try {
  const response = await axios.get('https://example.com/invalid-endpoint');
} catch (err) {
  if (err.response) {
    // Server returned an error response
    console.log('Status code:', err.response.status);
  } else if (err.request) {
    // Request was sent but no response was received
    console.log('No response from server:', err.request);
  } else {
    // Error setting up the request
    console.log('Request setup failed:', err.message);
  }
}

Case 3: Custom Functions Throwing Errors #

If you’re writing your own functions, you need to manually attach the statusCode to the error when throwing it:

async function fetchData() {
  try {
    // Simulate a failed operation
    throw new Error('Resource not found');
  } catch (err) {
    // Add status code to the error
    err.statusCode = 404;
    throw err;
  }
}

// When calling the function
try {
  await fetchData();
} catch (err) {
  if (err.statusCode) {
    console.log('Status code:', err.statusCode);
  } else {
    console.log('Generic error:', err.message);
  }
}

Key Takeaway #

First, check what type of error you’re dealing with. Log the entire err object to the console (console.log(err)) to see its structure – this will tell you exactly where the status code is stored (if it exists at all).

内容的提问来源于stack exchange，提问作者pavithra prabodha