What is the fastest way to generate a random integer in javascript?

This code is faster... to type.

var random_integer = Math.random()*101|0;

It won't work right for huge numbers though.

(and it doesn't run any faster, at least not in chrome.)

You could achieve a much faster speed during the game if you generate the random numbers beforehand, though.

for (var i=1e6, lookupTable=[]; i--;) {
  lookupTable.push(Math.random()*101|0);
}
function lookup() {
  return ++i >= lookupTable.length ? lookupTable[i=0] : lookupTable[i];
}

lookup will rotate through an array with a million random integers. It is much faster than calling random and floor (of course, there is a "loading time" penalty up front from generating the lookup table).

If you want to avoid floating point calculation then you can do that by writing your own pseudo random number generator. Here is a list of well known pseudo random number generators (PRNG). Linear congruential generator is the easiest one to implement and probably most effective in terms of performance too. However, you will need to understand the theory behind PRNGs well enough to write an effective one. That might not be worth of effort though. The JS implementation should be effective enough. At the end there is a high possibility that you will find Math.random() is running faster than your code.

i mostly use

    var a = Math.floor(Math.random((number you'd like to be minimum, (number you'd like to be maximum) * (number you'd like to be maximum);