Resizing image in user side in Vue CLI JavaScript

image-resize.js

/**
 * Resizing image in user side
 * @param {string} filePath - file input value
 * @param {number} [max_width=1600] - result image max width
 * @param {number} [max_height=900] - result image max height
 * @returns {Promise<base64string>}
 */
export default (filePath, max_width, max_height) => {
    /**
     * Example
     * import imageResize from 'image-resize'
     * ...
     * methods: {
     *       fileInputChange: function (object) {
     *           const file = object.target.files[0];
     *           imageResize(file).then(fileB64 => {
     *              console.log(fileB64); // resized image in base 64 encoding
     *           });
     *       }
     * }
     * ...
     */
    return new Promise((resolve, reject) => {
        const canvas = document.createElement("canvas");
        if (canvas.getContext) {//checking if canvas object supported in browser
            const img = document.createElement("img");
            img.src = window.URL.createObjectURL(filePath);
            img.onload = function () {
                window.URL.revokeObjectURL(this.src);
                if (!max_width) {
                    max_width = 1600;
                }
                if (!max_height) {
                    max_height = 900;
                }
                let width = img.width;
                let height = img.height;

                if (width > max_width) {
                    height *= max_width / width;
                    width = max_width;
                }
                if (height > max_height) {
                    width *= max_height / height;
                    height = max_height;
                }

                canvas.width = width;
                canvas.height = height;
                const ctx = canvas.getContext("2d");
                ctx.drawImage(img, 0, 0, width, height);
                resolve(canvas.toDataURL('image/jpeg', .9));
            }
        } else {
            reject(new Error('Canvas not supported'));
        }
    })

}