(function () { const MAX_NUM = 10000; // パーティクルの個数 const STAGE_W = 465; const STAGE_H = 465; const FRICTION = 0.96; const ACC_VALUE = 50; /** * パーティクルクラスです。 * @param {number} x * @param {number} y * @constructor */ class Particle { constructor(x, y) { this.x = x; this.y = y; this.vx = 0; this.vy = 0; } } function updateParticlePosition(particle, gravityX, gravityY) { const diffX = gravityX - parti