Question

46

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

rated 0 times [ 51] [ 5] / answers: 1 / hits: 27097 / 13 Years ago, sun, january 8, 2012, 12:00:00

Normally this is how you get a random number in javascript.

Math.random();

However, this method seems to be inefficient when it comes to generating random integers.

Firstly, the random function has to generate a random decimal, like 0.1036098338663578, then it has to be multiplied to a suitable range (10.464593220502138). Finally, the floor function subtracts the decimals to produce the result (which in this case, 10).

var random_integer = Math.floor(Math.random()*101);

Is there a faster way to generate random integers in javascript?

Edit1:

I am using this for creating a canvas HTML5 game. The FPS is about 50, and my code is pretty optimized, apart from generating a random number.

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pariss

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2 Years ago

answered 13 Years ago alorac · Accepted Answer

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).