index.js

const canvasModule = require("canvas");
const webp = require("./build/Release/canvaswebp.node").canvasToBufferWebp;

// 1.x : 2.x
const Canvas = typeof canvasModule === "function" ? canvasModule : canvasModule.Canvas;

const oToBuffer = Canvas.prototype.toBuffer;

Canvas.prototype.toBuffer = function (format, config, callback) {
	if (format === "image/webp") {
		config = config || {};
		let quality = typeof config.quality === "number" ? config.quality * 100 : 90;
		quality = Math.min(quality, 100);
		quality = Math.max(quality, 0);
		const lossless = typeof config.lossless === "boolean" ? config.lossless : true;

		let error = null, encoded;
		try {
			encoded = webp(this, quality, lossless);
		} catch (ex) {
			error = ex;
		}

		if (typeof callback === "function") {
			// pseudo-async
			process.nextTick(() => callback(error, encoded));
		} else {
			if (error) throw error;
			return encoded;
		}

	} else {
		return oToBuffer.call(this, format, config, callback);
	}
};