How does Node's console module implement console output?

Node.js (Node for short) is a runtime environment based on Chrome JavaScript. Node enables JavaScript to run on the server side, replacing traditional server-side scripting languages ​​such as PHP, Python, etc. In Node, there is a basic module console that can output information directly on the console.

This article will introduce how to use Node's console module to achieve console output, as well as common uses of this module.

1. Import of console module

In Node, you need to import the console module into your program through the require() function. As shown below:

const console = require('console');

2. Basic usage of console

The basic usage of console is basically the same as the console in the browser, as shown below:

1. In Text information is output on the console:

console.log('Hello, world!');

2. Warning information is output on the console:

console.warn('This is a warning!');

3. Error information is output on the console:

console.error('This is an error!');

4. Output information on the console and use placeholders:

console.log('My name is %s, and I am %d years old.', 'Tom', 18);

The usage of placeholders is as follows:

%s：输出字符串；
%d：输出数字；
%j：输出JSON格式的对象；
%o：输出一个对象；
%%：输出一个百分号。

5. In control Station output object:

let obj = {name: 'Tom', age: 18};
console.dir(obj);

6. Output timing information on the console:

console.time('test');
//执行一些操作
console.timeEnd('test');

3. Advanced console usage

In addition to the above basic methods , the console also has more advanced methods that can facilitate us to debug and output information.

1. console.assert()

console.assert() method is used to determine whether a certain condition is true. If it is false, an error is output on the console. information.

console.assert(2 === 1, '2不等于1，请检查代码！');

2. console.count()

The console.count() method can count the output text and output the counting results on the console.

for(let i = 0; i < 5; i++) {
    console.count('count');
}

3. console.group() & console.groupEnd()

The console.group() and console.groupEnd() methods can display the output information in groups.

console.group('group');
console.log('Hello');
console.log('World');
console.groupEnd();

4. console.table()

The console.table() method can display the output content in the form of a table.

let arr = [{name: 'Tom',age: 18}, {name: 'Jerry', age: 20}];
console.table(arr);

4. Summary

Through the study of this article, we have learned how to use the console module in Node, including basic usage and advanced usage. The console module can facilitate us to debug and output information, and improve development efficiency.

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