Modifier key tracking in JavaScript

Using the Event object, you can find out if the Ctrl, Alt, and Shift keys were pressed at the time of the event. This is done using the properties ctrlKey, altKey and shiftKey - they have the value true or false depending on whether this key was pressed at the time of the event or not.

Let's look at an example. Let's say we have the following button:

<button id="elem">text</button>

By clicking on the button, we will display a message about whether one of the keys Ctrl, Alt and Shift was pressed:

let elem = document.querySelector('#elem');

elem.addEventListener('click', function(event) {
	if (event.ctrlKey) {
		console.log('Ctrl is pressed');
	}
	
	if (event.altKey) {
		console.log('Alt is pressed');
	}
	
	if (event.shiftKey) {
		console.log('Shift is pressed');
	}
});

Given an element. Make it turn red when clicked, but only if the Alt key is pressed at the time of the click.

Let's say you have the list ul with tags li:

<ul id="elem">
	<li>text</li>
	<li>text</li>
	<li>text</li>
	<li>text</li>
	<li>text</li>
</ul>

Make it so that when you click on any li, the number 1 is added to the end of its text if the Ctrl key is pressed, and the number 2 if Shift is pressed.