nodejs_stream_transformer_example.js

"use strict";

/*
    data.txt:
    1
    2
    3
    4
    5
    6
 */

const fs = require('fs');
const Transformer = require('stream').Transform;

let stream = fs.createReadStream('data.txt');

let gt3 = (chunk)=> {
    let partial = [];
    let str = chunk.toString().split(/\n/);

    for (let i = 0, len = str.length; i < len; i++) {
        if (str[i] > 3) {
            partial.push(str[i]);
        }
    }

    return new Buffer(partial.join('\n'));
};

class Input extends Transformer {
    _transform(chunk, encoding) {
        this.push(gt3(chunk));
    }
}

const input = new Input();

stream.pipe(input);

input.on('data', (chunk)=> {
    console.log(chunk.toString());
});