Javascriptで画像リサイズ(縮小) - Qiita

/** * @param {HTMLImageElement} imgEL * @param {Number} maxSize * @return {Promise<Blob>} */ const resizeImage = (imgEL, maxSize, type = 'image/png') => new Promise((resolve) => { const ratio = imgEL.naturalWidth / imgEL.naturalHeight const canvas = document.createElement('canvas') canvas.width = ratio >= 1 ? maxSize : maxSize / ratio canvas.height = ratio < 1 ? maxSize : maxSize / ratio canvas.ge