It's easy in Python.

>>> import random
>>> random.choice(['red','green','blue'])
'green'

The reason the code you're looking at is so common is that typically, when you're talking about a random variable in statistics, it has a range of [0,1). Think of it as a percent, if you'd like. To make this percent suitable for choosing a random element, you multiply it by the range, allowing the new value to be between [0,RANGE). The Math.floor() makes certain that the number is an integer, since decimals don't make sense when used as indices in an array.

You could easily write a similar function in Javascript using your code, and I'm sure there are plenty of JS utility libraries that include one. Something like

function choose(choices) {
  var index = Math.floor(Math.random() * choices.length);
  return choices[index];
}

Then you can simply write choose(answers) to get a random color.

It's a simple one-liner:

const randomElement = array[Math.floor(Math.random() * array.length)];

For example:

const months = ["January", "February", "March", "April", "May", "June", "July"];

const random = Math.floor(Math.random() * months.length);
console.log(random, months[random]);

The Math.random^[MDN] function chooses a random value in the interval [0, 1). You can take advantage of this to choose a value randomly.

var chosenValue = Math.random() < 0.5 ? value1 : value2;