const stream = require('stream');
Readable
()const stream = new stream.Readable();
const data = ['1', '2', '3'];
stream._read = function(){
if (data.length){
setTimeout(function(){
stream.push(data.shift());
}, 200);
} else {
stream.push(null);
}
};
stream.pipe(process.stdout);
Transform
()const tr = new stream.Transform();
tr._transform = function(chunk, enc, cb){
var string = String(chunk);
this.push(string);
cb();
};
process.stdin
.pipe(tr)
.pipe(process.stdout);