How to make an infinite loop in Javascript

I would like to have a toggle button that runs a function until it's pressed again. I have some code for the toggle:

const backgroundButton = document.getElementById("backgroundButton"); //getting button from HTML
let clickToggle = 0; //defining a veriable used to store the state of the button


backgroundButton.addEventListener("click", function(){   
    if (clickToggle == 0) {

        console.log('button was off');

        //start loop

        clickToggle = 1;
    }
    else {

        console.log('button was on');
        
        //stop loop
        
        clickToggle = 0;
    }
});

But I don't know how to create an infinite loop that does not crash.

You could use setInterval and clearInterval. A truly infinite loop would look like this:

while (true) doSomething();

But that is not what anyone wants, as it will block the user interface. Using setTimeout or setInterval you allow the event loop to continue to do its work.

I'll assume you want to repeat calling the function doSomething in this demo:

const backgroundButton = document.getElementById("backgroundButton"); 
let timer = 0;
const output = document.getElementById("output");

backgroundButton.addEventListener("click", function(){   
    if (timer == 0) {
        console.log('button was off');
        //start loop
        timer = setInterval(doSomething, 50);        
    }
    else {
        console.log('button was on');
        //stop loop
        clearInterval(timer);
        timer = 0;
    }
});

function doSomething() {
    output.textContent = +output.textContent + 1;
}

<button id="backgroundButton">Start/Stop</button>
<div id="output"></div>