Node.js 流可写。_write()方法
原文:https://www . geesforgeks . org/node-js-stream-write-_ write-method/
可写。_write()方法是 Stream 模块的内置应用编程接口，用于实现可写流。可写的。_write()方法在定义它的类中加上了下划线。此外，用户程序不能直接调用它。此方法通过使用子类实现，并且仅由内部可写类方法调用。
语法:
writable._write( chunk, encoding, callback )
参数:该方法接受三个参数，如上所述，如下所述:
- 区块:是要写入的数据，可以是缓冲区、字符串或任何类型。
- 编码:如果区块是字符串类型，则使用的编码类型。
- 回调:是检查写操作完成还是失败而调用的方法。如果调用没有成功，传递给回调的第一个参数必须是“Error”对象，如果写入成功，则为 null。
下面的例子说明了可写的用法。_write()方法 Node.js:
例 1:
// Node.js program to demonstrate the
// writable._write() method
// Constructing writable stream
const {Writable} = require("stream");
// Function to check char
const charchecks = new Writable({
// Implementing write function
write(chunk, encoding, callback){
// Defining string
const string = chunk.toString();
// If string contains below character
// then an error is show else the
// written string is returned
if(string.includes("\/")){
callback(Error("Forbidden character"));
}
else
{
// Displays string
console.log(string);
callback();
}
}
});
// Piping standard input to standard output, if
// you don't enter the forbidden character else
// it throws error
process.stdin.pipe(charchecks).on('error', console.log);
// Enter the string to be written
console.log("Enter the string: ");
现在，您需要运行代码并在运行时输入字符串来获得输出。
Enter the string:
GeeksforGeeks
GeeksforGeeks // Output
Enter the string:
GfG
GfG // Output
Enter the string:
Nidhi
Nidhi //Output
现在，要退出它，你需要按下 control + C。
例 2:
// Node.js program to demonstrate the
// writable._write() method
// Constructing writable stream
const {Writable} = require("stream");
// Function to check char
const charchecks = new Writable({
// Implementing write function
write(chunk, encoding, callback){
// Defining string and encoding it
const string = chunk.toString('hex');
// Prints encoded string
console.log(string);
// If the encoded string contains below
// character then an error is shown else
// the length of the encoded string is
// returned
if(string.includes("c")){
callback(Error("This is an error."));
}
else
{
// Displays length of the encoded string
console.log(string.length);
callback();
}
}
});
// Piping standard input to standard output, if
// you don't enter the forbidden character else
// it throws an error
process.stdin.pipe(charchecks).on('error', console.log);
// Enter the string to be written
console.log("Enter the string: ");
现在，您需要运行代码并在运行时输入字符串来获得输出。 输出:
Enter the string:
Geeks
4765656b730a // encoded string
12 // length of encoded string
Nidhi
4e696468690a
12
portal
706f7274616c0a // encoded string contains "c" so length of it
// is not returned and an error is thrown
Error: This is an error.
at Writable.write [as _write] (/home/runner/QuickwittedDistantCensorware/index.js:25:16)
at doWrite (_stream_writable.js:415:12)
at writeOrBuffer (_stream_writable.js:399:5)
at Writable.write (_stream_writable.js:299:11)
at ReadStream.ondata (_stream_readable.js:710:20)
at ReadStream.emit (events.js:198:13)
at ReadStream.EventEmitter.emit (domain.js:448:20)
at addChunk (_stream_readable.js:288:12)
at readableAddChunk (_stream_readable.js:269:11)
at ReadStream.Readable.push (_stream_readable.js:224:10)
现在，要退出它，你需要按 control C. 所以，这里抛出一个错误，因为运行时输入包括所述的禁止字符，所以，抛出一个错误。
参考:https://nodejs . org/API/stream . html # stream _ write _ write _ chunk _ encoding _ callback _ 1
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