[Solved]-Bisecting an array of objects: are not all of them enumerated?-d3.js

This is the expected behaviour.

If you look at the source code for d3.bisector, you'll see that it does not iterate the whole array the way you think. Have a look here:

while (lo < hi) {
    var mid = lo + hi >>> 1;
    if (compare(a[mid], x) > 0) hi = mid;
    else lo = mid + 1;
}

The interesting part lies here: var mid = lo + hi >>> 1;. What this bitwise (named zero-fill right shift) does is calculating the midpoint of the array.

In your case, the array has 78 elements. Therefore:

console.log(0 + 78 >>> 1)

And it keeps getting the midpoint of the remaining part, again and again, until finding the element. Have a look here:

let lo = 0,
  hi = 78;
while (lo < hi) {
  let mid = lo + hi >>> 1;
  console.log(mid)
	lo = mid + 1;
}

For an array of 78 elements it does that 6 times (not 5, as you mentioned), and that's why you see the console.log working only 6 times.

Have a look at this demo, an array of 78 elements, the console.log works 7 times:

const data = d3.range(78);

const bisect = d3.bisector(function(d) {
  console.log(d);
  return d;
}).left;

bisect(data, 5);

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/5.7.0/d3.min.js"></script>

Now let's increase the array to 1000 elements. The console.log works 10 times:

const data = d3.range(1000);

const bisect = d3.bisector(function(d) {
  console.log(d);
  return d;
}).left;

bisect(data, 5);

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/5.7.0/d3.min.js"></script>