Math.floor() always rounds toward negative infinity — the largest integer <= input. Widely used for generating random integers, computing page numbers, and working with pixel coordinates. Math.floor(-4.1) = -5, not -4.

Available since ES1 (1997). Behavior is fully standardized and identical across all browsers and Node.js.

• Math.floor(-4.1) === -5, not -4 — rounds toward -∞
• random int from 0 to N-1: Math.floor(Math.random() * N)
• bitwise OR (x | 0) is faster but only works within 32-bit int range.