Indeed, the Javascript code is much larger. But the description tells you. "Terrain rendering algorithm in less than 20 lines of code" So, it just means, that

Indeed, the Javascript code is much larger. But the description tells you. "Terrain rendering algorithm in less than 20 lines of code" So, it just means, that a clean implementation of the terrain rendering algorithm takes 20 lines. With initialization, keyboard handling, map selection, collision detection, fps display and some JavaScript optimizations it needs much more lines of code.