What does nodejs use to output logs?

Node.js is an open source server-side JavaScript runtime environment that can be used to build efficient network applications. When running nodejs applications, output logs are very important, as they can help developers quickly locate and solve problems.

Node.js provides a variety of ways to output logs. This article will introduce some common methods.

1. console.log

console.log is the most basic log output method of Node.js, which can output logs to the console. For example:

console.log('Hello World!');

Running the above code will output 'Hello World!' to the console.

console.log can also receive multiple parameters, separated by commas. For example:

console.log('Hello', 'World!');

Running the above code will output 'Hello World!' to the console.

2. console.error

console.error can also output the log to the console, but it outputs error information. For example:

console.error('Error: Something went wrong!');

Running the above code will output 'Error: Something went wrong!' on the console.

console.error can also receive multiple parameters, separated by commas.

3. console.warn

console.warn outputs warning information. For example:

console.warn('Warning: This can cause unexpected behavior!');

Running the above code will output 'Warning: This can cause unexpected behavior!' on the console.

4. console.info

console.info outputs a common message, usually used to record some important operations. For example:

console.info('Info: The server has started!');

Running the above code will output 'Info: The server has started!' on the console.

5. console.dir

console.dir can output a property list of an object. For example:

let obj = { name: 'Bob', age: 30, gender: 'male' };
console.dir(obj);

Run the above code, the following information will be output on the console:

{ name: 'Bob', age: 30, gender: 'male' }

6. Use a third-party log library

In addition to Node.js In addition to the console object provided, developers can also use third-party logging libraries, such as winston, log4js, etc. These log libraries provide richer functions, such as supporting output to files, supporting output by level, etc.

For example, use winston to output the log:

const winston = require('winston');

const logger = winston.createLogger({
  level: 'info',
  format: winston.format.json(),
  defaultMeta: { service: 'user-service' },
  transports: [
    new winston.transports.Console(),
    new winston.transports.File({ filename: 'error.log', level: 'error' }),
    new winston.transports.File({ filename: 'combined.log' })
  ]
});

logger.info('Hello World!');

Run the above code, 'Hello World!' will be output on the console, and logs will be recorded in error.log and combined.log.

To sum up, Node.js provides a variety of ways to output logs, and developers can choose the appropriate method according to their own needs. If you need richer functions, you can choose to use a third-party log library.

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