【JavaScript】数値のカウントアップ・ダウン - Qiita

class Counter { #defaults #options #easings #counterList constructor(config) { this.#defaults = { selector: '.js-counter', duration: 2000, easing: null, inviewClass: 'is-inview' } this.#options = { ...this.#defaults, ...config } this.#easings = { easeOutQuad: (t) => t * (2 - t), easeOutCubic: (t) => --t * t * t + 1, easeOutQuart: (t) => 1 - --t * t * t * t, easeOutQuint: (t) => 1 + --t * t * t * t