electron-window-resize.ts

// Count in "frames", actually it's more ticks
const DEFAULT_DURATION = 150;

/* Penner easing function
See: http://robertpenner.com/easing/ */
const DEFAULT_EASING = (t, b, c, d) => (t == d ? b + c : c * (-Math.pow(2, (-10 * t) / d) + 1) + b);

type BrowserWindowAnimateOptions = {
	duration?: number;
	easing?: typeof DEFAULT_EASING;
};

const windowSetSize = BrowserWindow.prototype.setSize;
BrowserWindow.prototype.setSize = function (
	this: BrowserWindow,
	width: number,
	height: number,
	animate?: boolean | BrowserWindowAnimateOptions
) {
	if (animate) {
		const [startWidth, startHeight] = this.getSize();
		const [targetWidth, targetHeight] = [width, height];

		const animateOptions =
			typeof animate === "object" ? animate : { duration: DEFAULT_DURATION, easing: DEFAULT_EASING };

		const duration = animateOptions.duration ?? DEFAULT_DURATION;
		const easing = animateOptions.easing ?? DEFAULT_EASING;

		let currentFrame = 0;
		const updateSize = () => {
			currentFrame++;
			windowSetSize.apply(this, [
				Math.round(easing(currentFrame, startWidth, targetWidth - startWidth, duration)),
				Math.round(easing(currentFrame, startHeight, targetHeight - startHeight, duration)),
			]);
			if (currentFrame < duration) setImmediate(updateSize);
		};
		setImmediate(updateSize);
	} else {
		windowSetSize.apply(this, [width, height]);
	}
};

declare module "electron" {
	interface BrowserWindow {
		setSize(width: number, height: number, animate?: boolean | BrowserWindowAnimateOptions);
	}
}

main.ts

function createWindow() {
	const win = new BrowserWindow({
		width: 100,
		height: 100,
		title: "Eletron App",
		webPreferences: {
			preload: join(__dirname, "preload.js"),
		},
	});

	win.loadFile("index.html");

	win.on("show", () => {
		/* Old fashion way still works, but for all platforms
    win.setSize(800, 600, true); */
		win.setSize(800, 600, { duration: 500 });
	});

}

// Whatever's next...