how to handle crashes assocaiated with memory allocation in nodejs?

Calling setInterval with no time, this is adding to the callback queue as fast as possible, without any limits. And if you add items to a queue faster than you can remove them, memory will always grow.

*Edit: to understand exactly what happens with the event loop and callback queue when you do a setInterval, I recommend watching the excellent JSConf talks by Philip Roberts and/or Jake Archibald.

You have a few options. You could change to a setTimeout, and then invoke another setTimeout in your .then, once the last call has finished. This would essentially serialize it.

A more nuanced approach would be to limit the max number of concurrent mongoDB writes by using a counter. That way you can have a certain number of writes happening concurrently. In this example, it limits the number of concurrent writes to 10. This should keep your memory from growing without limits.

const faker = require("faker")
let userName; 
let email; 
let numRunning = 0;
let maxRunning = 10;

setInterval(async () => {
  if (numRunning > maxRunning) return;
  numRunning++;
  userName = faker.name.findName(); 
  email = faker.internet.email(); 
  await User.create({
    userName: createdUser.userName,
    age: createdUser.age,
  })
    .then(() => {
      numRunning--;
      //getting memory usage
      console.log(process.memoryUsage().heapUsed / 1024 / 1024);
    })
    .catch(err => {
      numRunning--;
      console.log(err);
    });
}, 50);

I also added an interval of 50ms. A zero for a setInterval really isn't a good idea. There are good reasons to sometimes use a zero for setTimeout, but I can't think of a good reason to ever use a zero for a setInterval.