writable._construct(callback)

• callback <Function> 当流完成初始化时,调用此函数(可选择传入错误参数)。

_construct() 方法不能被直接调用。它可以由子类实现,如果实现了,也只会被内部的 Writable 类方法调用。

🌐 The _construct() method MUST NOT be called directly. It may be implemented by child classes, and if so, will be called by the internal Writable class methods only.

在流构造函数返回之后,这个可选函数将在一个时间片中被调用,从而延迟任何 _write()、_final() 和 _destroy() 的调用,直到调用 callback。这对于在流可用之前初始化状态或异步初始化资源非常有用。

🌐 This optional function will be called in a tick after the stream constructor has returned, delaying any _write(), _final() and _destroy() calls until callback is called. This is useful to initialize state or asynchronously initialize resources before the stream can be used.

const { Writable } = require('node:stream');
const fs = require('node:fs');
class WriteStream extends Writable {
 constructor(filename) {
 super();
 this.filename = filename;
 this.fd = null;
 }
 _construct(callback) {
 fs.open(this.filename, 'w', (err, fd) => {
 if (err) {
 callback(err);
 } else {
 this.fd = fd;
 callback();
 }
 });
 }
 _write(chunk, encoding, callback) {
 fs.write(this.fd, chunk, callback);
 }
 _destroy(err, callback) {
 if (this.fd) {
 fs.close(this.fd, (er) => callback(er || err));
 } else {
 callback(err);
 }
 }
} 拷贝