index.js

let buffer = '';

for (let i = 0; i < 1e6 * 512; i++) {
  buffer += String.fromCharCode(65 + Math.floor(Math.random() * 26));

  if (i % 1e6 === 0) {
    console.log(Math.floor(process.memoryUsage().heapUsed / 1024 / 1024), 'MB heap is used');
  }
}

output.txt

$ node --max-old-space-size=128 index.js
4 'MB heap is used'
44 'MB heap is used'
81 'MB heap is used'
120 'MB heap is used'
159 'MB heap is used'
197 'MB heap is used'
235 'MB heap is used'
273 'MB heap is used'
311 'MB heap is used'
349 'MB heap is used'
387 'MB heap is used'
425 'MB heap is used'
463 'MB heap is used'
501 'MB heap is used'
539 'MB heap is used'
577 'MB heap is used'