I am using lodash memonized function and is noticing some strange behavior that does not make sense to me.

const memonizedPadStart = _.memoize((k, l) => String(k).padStart(l, '0'));
const innerHelper = _.memoize((value) => {
  // Somewhere have padStart
  // Option 1 cache
  const str = memonizedPadStart(k, l);

  // Option 2 normal
  const str = String(k).padStart(l, '0'));
});
const generate = _.memoize((str) => {
  // Somewhere we call innerHelper
  ... 
  const results = innerHelper(value);
  ...
});


// Preprocessing.
for (let i = 0; i < list.length; i += 1) {
  const results = generate(list[i].str);
  for (let j = 0; j < results.length; j += 1) {
  }
}

// Now we test performance
let totalLoopTime = 0n;
let totalFunctionTime = 0n;
for (let i = 0; i < list.length; i += 1) {

  const functionStart = process.hrtime.bigint();
  const results = generate(list[i].str);
  const functionTaken = process.hrtime.bigint() - functionStart;
  totalFunctionTime += functionTaken;

  const loopStart = process.hrtime.bigint();
  for (let j = 0; j < results.length; j += 1) {
  }
  const loopTaken = process.hrtime.bigint() - loopStart;
  totalLoopTime += loopTaken;
}
console.log('totalFunctionTime', Number(totalFunctionTime)/1000000, 'ms');
console.log('totalLoopTime', Number(totalLoopTime)/1000000, 'ms');

Here is the odd thing, if I use Option 1, commenting out Option 2

totalFunctionTime 0.394859 ms
totalLoopTime 7.859825 ms

If I use Option 2

totalFunctionTime 0.506823 ms
totalLoopTime 19.078935 ms

I am very confused, Option 1 and Option 2 should not yield different results because the upper function already been memonized so it does not get called at all (I have verified this by logging)

And it seems that it affects loop timing? Which has nothing to do with Option 1 and Option 2 at all. T Note this test case is using plain loop (nothing is happening inside the loop)

Anyone can provide reason for this?