nodejs Chinese error reporting

Node.js is a popular JavaScript runtime environment for building efficient web and server-side applications. During the development process, it is very common to encounter errors, but encountering errors in Chinese may cause some inconvenience to users. In this article, I will introduce Chinese errors and solutions that may be encountered in Node.js to help readers optimize the development experience.

1. SyntaxError: Invalid or unexpected token

During the development process, we sometimes encounter errors such as "Invalid syntax" or "Unexpected token". At this time, it is most likely caused by the appearance of Chinese characters. For example:

var 变量名 = 1;

Browsers can usually parse this kind of code, but Node.js will throw a SyntaxError: Invalid or unexpected token error because the variable name contains Chinese characters.

Solution: Try to avoid using Chinese characters in variable names, function names or other identifiers, and use English characters or underscores instead.

2. TypeError: Cannot read property 'xx' of null/undefined

This is one of the more common errors in Node.js development. This error occurs when we try to read properties on null or undefined objects, or when we try to call their methods.

Common code examples:

var obj = null;
console.log(obj.xxx);

This code will throw TypeError: Cannot read property 'xxx' of null error. Similarly, trying to call an undefined function will produce a similar error:

var fn = undefined;
fn();

At this time, Node.js will throw a TypeError: Cannot read property 'call' of undefined error.

Solution: Before using an object or calling a function, first ensure that the object exists or the function is defined. You can use the if statement combined with the typeof operator to determine whether the object exists or whether the function is defined:

if (typeof obj !== 'undefined' && obj !== null) {
  console.log(obj.xxx);
}

if (typeof fn === 'function') {
  fn();
}

3. SyntaxError: Identifier 'variable name' has already been declared

In When using let or const to declare a variable, if the same variable is defined repeatedly, Node.js will throw a SyntaxError: Identifier 'variable name' has already been declared error. For example:

let name = 'Tom';
let name = 'Jerry'; // 报错：SyntaxError: Identifier 'name' has already been declared

Solution: Use unique variable names, or change let/const to var keyword.

4. ReferenceError: x is not defined

This type of error often occurs when the variable name or function name is not defined. For example:

// 未定义的变量
console.log(x);

// 未定义的函数
y();

At this time, Node.js will throw ReferenceError: x is not defined or ReferenceError: y is not defined error.

Solution: Make sure the variable name or function name has been correctly defined, or avoid operating on undefined variables or functions.

5. TypeError: xxxx is not a function

When calling a method, if the method is not a function, Node.js will throw TypeError: xxxx is not a function error. For example:

let obj = {};
obj.fun(); // 报错：TypeError: obj.fun is not a function

This code attempts to call the fun method of object obj, but in fact obj does not have a method named fun.

Solution: Check whether the called method exists, or ensure that the object's property value is indeed a function.

Summary

In the development process of Node.js, it is very common to encounter errors. But many times, these mistakes can be avoided by following the rules and writing your code carefully. Through the introduction of this article, I believe that readers will have a deeper understanding of Chinese error reporting in Node.js, and I hope it will be helpful to readers.

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