TILK the default random number generator uses the JavaScript Math.random.
Returns a Number value with positive sign, greater than or equal to 0 but less than 1, chosen randomly or pseudo randomly with approximately uniform distribution over that range, using an implementation-dependent algorithm or strategy. This function takes no arguments.
Each Math.random function created for distinct code Realms must produce a distinct sequence of values from successive calls.
The actual implementation of this method differs from browser to browser. I believe Chrome uses the xorshift128+ algorithm for this. All psuedo random number generators require a seed, the difference here being that the JS Math.random method doesn't allow you to choose a seed. It is chosen by the browser using a source of randomness provided by the operating system.
We use xorshiro256** for our random number generator, which is of the same family as xorshift128+. I would expect the quality levels to be fairly similar to the Chrome one. I will note neither of these methods are considered "cryptographically secure" but that doesn't mean the quality is poorer. It just means that you cannot use the output of the generator to derive other values in the sequence ( before or after the current output ). They can still exhibit excellent pseudo randomness and distribution.