getActiveWindow allows you to get a Window reference of the system's focused window at the moment of the function call.
getActiveWindow will return as a Promise.

1const { getActiveWindow } = require('@nut-tree/nut-js');
2
3(async () => {
4    const windowRef = await getActiveWindow();
5})();

Now logging this alone wouldn't be very useful, remember that it's simply a reference:

1// source:
2//  ...
3    const windowRef = await getActiveWindow();
4    console.log(windowRef);
5//  ...
6
7// output:
8Window {
9  providerRegistry: DefaultProviderRegistry {
10  // ...
11  },
12  windowHandle: 2165090
13}

Instead, we want to take advantage of our window's title and region properties. Be careful though, these are getter properties that each return a Promise instead of a plain value - so we must use await again:

1const { getActiveWindow } = require('@nut-tree/nut-js');
2
3(async () => {
4    const windowRef = await getActiveWindow();
5    const title = await windowRef.title
6    const region = await windowRef.region
7    console.log(title, region)
8})();

You can also await these values in parallel instead of sequentially, as shown below:

1const { getActiveWindow } = require('@nut-tree/nut-js');
2
3(async () => {
4    const windowRef = await getActiveWindow();
5    const [title, region] = await Promise.all([windowRef.title, windowRef.region])
6    console.log(title, region)
7})();

Additionally, please note that this script will always detail the window information of the shell you run it from. To play around with getting the details of a different window, consider adding a delay before calling getActiveWindow. We can use nut.js' own sleep helper function to achieve this:

1const { getActiveWindow, sleep } = require('@nut-tree/nut-js');
2
3(async () => {
4    await sleep(4000) // delay for 4 seconds before continuing
5    const windowRef = await getActiveWindow();
6    const [title, region] = await Promise.all([windowRef.title, windowRef.region])
7    console.log(title, region)
8})();

1const { getActiveWindow, centerOf, randomPointIn, mouse, sleep } = require('@nut-tree/nut-js');
2
3(async () => {
4    const windowRef = await getActiveWindow();
5    const region = await windowRef.region
6    await mouse.setPosition(await centerOf(region))
7    await mouse.leftClick()
8    await sleep(1000)
9    await mouse.setPosition(await randomPointIn(region))
10    await mouse.leftClick()
11})();

1const { getActiveWindow } = require('@nut-tree/nut-js');
2
3(async () => {
4    setInterval(async () => {
5        const windowRef = await getActiveWindow()
6        const [title, region] = await Promise.all([windowRef.title, windowRef.region])
7        console.log(title, region.toString())
8    }, 2000)
9})();