If an array is the hovercraft, it can hold 4 billion "things" regardless of what those things are! So you need to fill that up to meet the requirements of the saying.
Ah but now we're at the crux of the issue; in Javascript, hovercrafts grow in size to accommodate as many eels as you put in, but to a maximum of ~4 billion. So "full" is not a question you can ask of your hovercraft, though it will tell you once it's overflowing.
What if we used a storage method that didn't grow?
In JavaScript we have typed arrays, we could use a `Uint16Array` to store UTF-16 code points as integers in each element, then we could define the amount of eels that our "hovercraft" could store ahead of time in a way that it won't expand.
const hovercraftEelCapacity = 331 // We can define our hovercraft to have room for 331 eels
const eel = 'eel'
const hovercraft = new Uint16Array(new ArrayBuffer(2 * eel.length * hovercraftEelCapacity)) // Each "eel" takes up 3 16-bit integers
for (let i = 0; i < hovercraftEelCapacity * eel.length; i += eel.length) {
hovercraft[i] = eel.codePointAt(0)
hovercraft[i+1] = eel.codePointAt(1)
hovercraft[i+2] = eel.codePointAt(2)
}
console.log('Your hovercraft full of eels: ', hovercraft)
