The Math.random() function returns a floating-point, pseudo-random number in the range [0, 1) that is, from 0 (inclusive) up to but not including 1 (exclusive), which you can then scale to your desired range. The implementation selects the initial seed to the random number generation algorithm; it cannot be chosen or reset by the user.
The Number.parseFloat() method parses a string argument and returns a floating point number. This method behaves identically to the global function parseFloat() and is part of ECMAScript 6 (its purpose is modularization of globals).