使用流將檔案讀入緩衝區

雖然使用 fs.readFile() 方法讀取檔案中的內容已經是非同步的，但有時我們希望在 Stream 中獲取資料而不是簡單的回撥。這允許我們將這些資料傳輸到其他位置，或者在結束時對其進行處理。

const fs = require('fs');

// Store file data chunks in this array
let chunks = [];
// We can use this variable to store the final data
let fileBuffer;

// Read file into stream.Readable
let fileStream = fs.createReadStream('text.txt');

// An error occurred with the stream
fileStream.once('error', (err) => {
    // Be sure to handle this properly!
    console.error(err); 
});

// File is done being read
fileStream.once('end', () => {
    // create the final data Buffer from data chunks;
    fileBuffer = Buffer.concat(chunks);
    
    // Of course, you can do anything else you need to here, like emit an event!
});

// Data is flushed from fileStream in chunks,
// this callback will be executed for each chunk
fileStream.on('data', (chunk) => {
    chunks.push(chunk); // push data chunk to array

    // We can perform actions on the partial data we have so far!
});