node . js Stream readable . unshift()方法
原文:https://www . geesforgeks . org/node-js-stream-readable-unshift-method/
可读流中的可读. unshift()方法用于将数据块推回到内部缓冲区。然而，当一个流被完全消耗并且需要“不消耗”时，这个方法是有帮助的。
语法:
readable.unshift( chunk, encoding )
参数:该方法接受两个参数，如上所述，如下所述。
- Block: It contains the data block to be unloaded into the read queue.
- Code: Save the code type.
返回值:该方法将数据块转移到内部缓冲区，再次调用 read 方法后可以只读。
以下示例说明了在 Node.js 中使用 readable.unshift()方法:
例 1:
// Node.js program to demonstrate the
// readable.unshift() method
// Including fs module
const fs = require('fs');
// Declaring data
var data = '';
// Constructing readable stream
const readable = fs.createReadStream("input.text");
// Instructions for reading data
readable.on('readable', () => {
let chunk;
// Using while loop and calling
// read method
while (null !== (chunk = readable.read())) {
// Displaying the chunk
console.log(`read: ${chunk}`);
}
});
console.log("Program ends!!!");
// Calling unshift method
readable.unshift(data);
输出:
Program ends!!!
true
read: GfG
例 2:
// Node.js program to demonstrate the
// readable.unshift(chunk[, encoding])
// method
// Include fs module
const fs = require('fs');
var data = '';
// Create readable stream
const readable = fs.createReadStream("input.text");
// Calling setEncoding method
readable.setEncoding('utf8');
// Instructions to unshift data
readable.on("readable", () => {
let data = readable.read();
while (data === "GfG") {
readable.unshift(data);
data = readable.read();
}
});
// Displays that program
// is unshifted
console.log("Unshifted!!");
输出:
Unshifted!!
参考:https://nodejs . org/API/stream . html # stream _ readable _ unshut _ chunk _ encoding。
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