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JavaScript Random

JS Random

Math.random() returns a random number between 0 (inclusive), and 1 (exclusive). Math.random() always returns a number lower than 1.

					 
        
          Math.random();

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Random Integer

Math.random() used with Math.floor() can be used to return random integers.

There is no such thing as JavaScript integers. We are talking about numbers with no decimals here.

					 
        
          Math.floor(Math.random() * 10);      // integer from 0 to 9
          Math.floor(Math.random() * 11);      // integer from 0 to 10
          Math.floor(Math.random() * 100);     // integer from 0 to 99
          Math.floor(Math.random() * 101);     // integer from 0 to 100
          Math.floor(Math.random() * 10) + 1;  // integer from 1 to 10
          Math.floor(Math.random() * 100) + 1; // integer from 1 to 100

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Proper Random Function

As you can see from the examples above, it might be a good idea to create a proper random function to use for all random integer purposes.

This JavaScript function always returns a random number between min and max.

					 
        
          // min (included) and max (excluded)
          function getRndInteger(min, max) {
            return Math.floor(Math.random() * (max - min) ) + min;
          }

          // both min and max (included)
          function getRndInteger(min, max) {
            return Math.floor(Math.random() * (max - min + 1) ) + min;
          }

Test Code Online

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