resize.js

const resizeToWidth = 800;
const resizeToHeight = 600;

const canvas = document.getElementById("canvas");
const image = document.getElementById("source");
const ctx = canvas.getContext("2d");

// Get *real* image size with naturalXXX
const {naturalWidth: imageWidth, naturalHeight: imageHeight} = image;

// Set the canvas to the desired size
canvas.width = resizeToWidth;
canvas.height = resizeToHeight;

// Paste our whole image on the the canvas
ctx.drawImage(image, 0, 0, resizeToWidth, resizeToHeight);