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Yesterday, I wrote a short article on generating random numbers in Javascript. The Javascript random number generator is similar to C/++ – it gives you a random number from 0 to 1 and you need to make it useful.

At the suggestion of a reader (thanks Justin), I decided to go ahead and turn the general formula for this into a short helper function to generate a random number.

Random Numbers: General Formula

First, let’s take a minute and recap the general formula for finding a random number.

Javascript’s Math.random() method returns a random number between 0 and 1. By multiplying this decimal value by a whole number, we can generate a desired range of values. For example, by multiplying Math.random()’s result by 10, we get a range of 0 to 10.

Next, we take the Math.floor value of that random number. This gives us just the integer portion – and it effectively cuts our range to 0 through 9. Finally, we can modify this by adding an offset number. So if we wanted a random number between 51 and 60, we’d add 51 to that result.

Creating a Random Number Function

The basic formula we end up with is…

(Math.floor( Math.rand() * setSize)) + setOffset;

Our code would be much more readable if we had a helper function that could be called like this…

randomNumber = rand(min, max);

Our function is going to take two parameters – min and max. From these two parameters, we can calculate the offset and the set size and generate the proper random number.

function rand(min, max) {
  var offset = min;
  var range = (max - min) + 1;
 
  var randomNumber = Math.floor( Math.random() * range) + offset;
  return randomNumber;
}

All done.

Add that function to a utility file, and you’ve got a handy random number generator at your disposal. It even uses the same format as PHP’s rand() function, to help increase consistency and readability in your code.

Tags: function, Game Design, javascript, math, random, snippet