nodejs character set conversion

Node.js is a very popular server-side JavaScript running environment. When writing Node.js applications, character set conversion is inevitably required. When dealing with Chinese, Japanese, Korean and other systems, character set conversion is necessary, which allows us to correctly handle text in various encoding formats.

In this article, we will introduce character set conversion in Node.js and how to use the iconv library for encoding conversion.

1. Overview of Character Sets

In computers, a character set is a scheme that maps characters to numerical codes. In practical applications, we usually use character encodings such as ASCII, Unicode, and UTF-8.

ASCII (American Standard Code for Information Interchange, American Standard Code for Information Interchange) is one of the earliest character encodings. It only supports English, numbers and a small number of special characters. ASCII encoding has a total of 128 characters, which are represented by 7 binary bits, with the highest bit being 0. ASCII encoding was later expanded to support more character sets, such as Latin-1, ISO-8859 series, etc.

Unicode is a globally unified character encoding scheme that includes all characters in various languages ​​around the world and assigns them unique codes. Unicode encoding has a total of 1,114,112 characters, of which the characters between 0x0000 and 0xFFFF correspond to a 16-bit encoding, called Basic Multilingual Plane (BMP) characters; and the characters between 0x010000 and 0x10FFFF correspond to a 32-bit encoding, called Auxiliary flat characters. Unicode encoding has multiple representation methods, such as UTF-8, UTF-16, etc.

UTF-8 (Unicode Transformation Format-8, Unicode Transformation Format 8-bit) is a variable-length Unicode encoding that can use 1 to 4 bytes to represent a character. It supports all Unicode characters . In UTF-8 encoding, ASCII characters are still represented by one byte, while non-ASCII characters such as Chinese characters are represented by 2 to 3 bytes. Therefore, it is compatible with ASCII encoding and can also save characters in various languages.

2. Node.js character set conversion

Node.js natively provides the Buffer class, which can store binary data in memory and is usually used in scenarios such as network transmission and file reading and writing. When we read binary data from external resources, we need to decode the character set and convert the binary data into a readable string; when we convert the string into binary data, we need to encode it and convert the characters is binary data.

Node.js provides some built-in character set conversion modules, such as buffer.toString(), Buffer.from(), etc., which can perform partial encoding conversion of binary data. For example:

const buf = Buffer.from('中文');
console.log(buf.toString('utf8')); // 中文
console.log(buf.toString('ascii')); // ��w�
console.log(buf.toString('base64')); // 5Lit5paH

In the above example, we convert a string 'Chinese' into a Buffer object and use the toString() method to convert it into other encoding formats. The utf8 encoding result is correct, but the ascii encoding and base64 encoding results are incorrect.

Node.js uses utf8 encoding by default for string conversion. If the character set to be converted is incompatible with utf8, you need to use a third-party library such as iconv for character set conversion.

3. Use the iconv library for character set conversion

iconv is a free open source C library used to convert between different character sets. There is an NPM module called iconv-lite in Node.js, which is a package of the iconv library and provides high-performance character set conversion functions.

Next, we will introduce how to use iconv-lite for character set conversion.

1. Install iconv-lite

First, we need to install iconv-lite.

npm install iconv-lite

2. String encoding conversion

Using iconv-lite to perform encoding conversion is very simple, we only need to call the corresponding method. For example, we convert a GB2312-encoded string to UTF-8 encoding:

const iconv = require('iconv-lite');
const str = '中文字符串';
const buf = iconv.encode(str, 'gb2312');
const str2 = iconv.decode(buf, 'utf8');
console.log(str2); // 中文字符串

In the above example, we first use the iconv.encode method to convert the GB2312-encoded string into a Buffer object, and then use The iconv.decode method converts the Buffer object into a UTF-8 encoded string. The converted string is a correct Chinese string.

3. Stream encoding conversion

When processing large files, you may need to use streams for encoding conversion. Here we can use the iconv-lite-stream library provided by iconv-lite to easily implement stream encoding conversion. For example, we convert a Shift_JIS encoded file to UTF-8 encoding:

const iconv = require('iconv-lite');
const fs = require('fs');
const iconvStream = iconv.decodeStream('Shift_JIS');
const inputStream = fs.createReadStream('shift-jis-file.txt');
const outputStream = fs.createWriteStream('utf8-file.txt');
inputStream.pipe(iconvStream).pipe(outputStream);

In the above example, we first create a readable stream, read the Shift_JIS encoded file, and then create a writable stream, Writes a UTF-8 encoded file. At the same time, we created a stream encoded as Shift_JIS through the iconv.decodeStream method, and chained it with the readable stream and the writable stream to achieve stream encoding conversion.

4. Summary

In this article, we introduced character set conversion in Node.js and how to use the iconv-lite library for encoding conversion. Character set conversion is a very necessary function when dealing with Chinese, Japanese, Korean and other systems. Correct use of character set conversion can effectively avoid problems such as garbled characters. We hope this article helps readers better understand character set conversion in Node.js.

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