stream transform

perf_hooks.js

const { PerformanceObserver, performance } = require('perf_hooks')

const getJSONParse = (data) => {
  performance.mark('getJSONParse init')
  JSON.parse(data)
  performance.mark('getJSONParse end')
  performance.measure('getJSONParse', 'getJSONParse init', 'getJSONParse end')
}

span.js

const { spawn } = require('child_process');

const child = spawn('wc');

process.stdin.pipe(child.stdin)

child.stdout.on('data', (data) => {
  console.log(`child stdout:\n${data}`);
});

transform.js

const {Transform} = require('stream')
const transform = new Transform({
  transform(chunk, encoding, callback) {
    this.push(chunk.toString().replace(/[1-9]/g,'*'))
    callback()
  }
})
process.stdin.pipe(transform).pipe(process.stdout)