How does Math.random() work in javascript?

Question

I recently figured out how to get a random number via google, and it got me thinking how does Math.random() work. So here I am I can not figure out how they did Math.random() unless they used a time like thing does anyone know how JavaScript's Math.random() works or an equivalent?

Answer 1

Math.random() returns a Number value with a 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.

Here's V8's implementation:

uint32_t V8::Random() {

    // Random number generator using George Marsaglia's MWC algorithm.
    static uint32_t hi = 0;
    static uint32_t lo = 0;

    // Initialize seed using the system random(). If one of the seeds
    // should ever become zero again, or if random() returns zero, we
    // avoid getting stuck with zero bits in hi or lo by reinitializing
    // them on demand.
    if (hi == 0) hi = random();
    if (lo == 0) lo = random();

    // Mix the bits.
    hi = 36969 * (hi & 0xFFFF) + (hi >> 16);
    lo = 18273 * (lo & 0xFFFF) + (lo >> 16);
    return (hi << 16) + (lo & 0xFFFF);
}

Source: http://dl.packetstormsecurity.net/papers/general/Google_Chrome_3.0_Beta_Math.random_vulnerability.pdf

Here are a couple of related threads on StackOverflow:

• Why is Google Chrome's Math.random number generator not *that* random?
• How random is JavaScript's Math.random?