Two conditions, both true

Two conditions must both say yes. The steps below call each condition a door. A row must pass both doors.

The rule

Two conditions joined by and keep a row only when both hold. Two conditions keep fewer rows, or the same — never more.

Here sectionAt and dueAt hold the section and due positions. The sign >= means is at least. One if sits inside the other. So a row is added only after passing both.

1. const sectionAt = headers.indexOf('section');
2. const dueAt = headers.indexOf('due');
3. if (row[sectionAt] === '9-A') {
4. if (row[dueAt] >= 1000) {
5. answer.push(row);
6. }
7. }

Every kept row also passed the first condition. So the second one cannot add rows.

On the full register, this keeps 4 of the 12 records. They are A-101, A-106, A-108 and A-110.

Ask for due at least 0, and all 7 of 9-A pass. Every due is at least 0. That is the same count, not fewer.

Pick a section and slide the due below. Read who passes both.

Fewer or the same — a second condition never adds a row.