nodejs error module

Node.js is a JavaScript runtime environment based on the Chrome V8 engine and is widely used to develop high-performance network applications. In Node.js, a variety of errors can occur that can affect the stability and reliability of your application. Therefore, Node.js provides an error module to help developers manage errors.

The errors module in Node.js provides some common error types. When using these error types, you only need to define the error class name and error message. Then, Node.js will automatically help us build an error object. When the error object is captured, we can easily obtain the error type, message and stack information to facilitate debugging and repairing the error.

This article introduces common error types in Node.js and how to use the error module to capture and manage errors.

Error types

In Node.js, the common error types are as follows:

Error

Error Yes The base class for all error types, it is a built-in JavaScript language object used to represent any type of error. When an uncaught exception occurs while Node.js is running, an Error object is thrown.

Example:

throw new Error('something went wrong');

TypeError

TypeError is a common error type that indicates that the variable or parameter type is wrong. When the runtime finds that the type of a variable or function parameter does not match the expected type, a TypeError error is thrown.

Example:

var n = null;
var result = n.toUpperCase();  // TypeError: Cannot read property 'toUpperCase' of null

RangeError

RangeError means that the variable exceeds the valid range or the array exceeds the legal range, for example, Array The index boundary is exceeded when accessing, Math exceeds the range when calculating, etc.

Example:

var arr = [1, 2, 3];
var n = arr[100];   // RangeError: Invalid array length

SyntaxError

SyntaxError Indicates code syntax errors, such as spelling errors, punctuation errors, missing parentheses, etc.

Example:

var n = 5;
if (n == 5 {    // SyntaxError: missing ) after condition
    console.log('value is 5');
}

EvalError

EvalError represents an error that occurred in the eval function.

Example:

try {
  eval('alert("Hello World)'); // EvalError: missing ) after argument list
} catch (err) {
  console.log(err.stack);
}

Error handling

When an error occurs, we can use the try...catch statement of Node.js to catch it Error, and then handle the error or throw the error.

try {
  // some code here
} catch (err) {
  // error handling here
}

At the same time, Node.js also provides some error handling methods:

1. process.on.

You can use process.on method to catch exceptions that are not caught by try...catch for final processing and recording.

process.on('uncaughtException', (err) => {
  console.log('Uncaught Exception');
  console.log(err.stack);
});

2. console.trace

console.trace method prints out the current call stack trace information, including the current location and function call stack .

function foo() {
  console.trace('trace function');
}

function bar() {
  foo();
}

bar();

Output:

Trace: trace function
    at foo (/path/to/file.js:2:11)
    at bar (/path/to/file.js:6:3)
    at Object.<anonymous> (/path/to/file.js:9:1)
    at Module._compile (internal/modules/cjs/loader.js:776:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:787:10)
    at Module.load (internal/modules/cjs/loader.js:643:32)
    at Function.Module._load (internal/modules/cjs/loader.js:556:12)
    at Function.Module.runMain (internal/modules/cjs/loader.js:839:10)
    at internal/main/run_main_module.js:17:11

3. assert

assert The module provides some assertion methods for use in programs Detect errors and exceptions.

var assert = require('assert');
var n = 5;
assert.ok(n == 5, 'n should be 5');

Conclusion

The error module of Node.js provides some common error types, as well as methods for handling exceptions that are not caught by try...catch. In Node.js applications, properly managing errors can improve the stability and reliability of the program and better help us find and fix error problems in a timely manner.

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