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JavaScript JavaScript Basics (Retired) Working With Numbers Create a random number

Posted by Danish Arif
Danish Arif
1,667 Points

Why not just use parseInt(Math.random()*6) + 1; ?

Am I missing something, or is it simple to just use parseInt(Math.random()*6) + 1;

Instead of, say, Math.Floor() or Math.Round() ...

Perhaps those are all good solutions, but they decided to go that route for the video? Hopefully someone with more Javascript knowledge can chime in.

1 Answer

Timothy Durward
Timothy Durward
3,242 Points
Timothy Durward
Timothy Durward
3,242 Points

Hello Danish, parseInt() interprets the argument as a string. Rule of thumb is to always Math.floor if that is your intention.

Timothy Durward
Timothy Durward
3,242 Points

This also explains the majority of of parseInt() https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt

Marcus Parsons
Marcus Parsons
15,719 Points

Exactly, Timothy. parseInt() is used to parse integers from strings. From the MDN, "If string is not a string [in reference to the first argument of parseInt()], then it is converted to one." So, what that means is that if you pass in numbers into parseInt, it will do this conversion: number -> string -> number. Math.floor(), however, doesn't have to do all of that type conversion for this statement because it only generates numbers and so, it is much faster. It just strips away the decimal points from whatever number it receives.

Rafael Valera
Rafael Valera
8,401 Points
Rafael Valera
Rafael Valera
8,401 Points

is it posible to cast whatever Math.random() returns to a whole number?

Marcus Parsons
Marcus Parsons
15,719 Points

That's the reason we use Math.floor(), which is to make it a whole number. Math.random() only returns values between 0 - 0.9999... which means that you have to use multiplication in order to get a higher maximum range out of Math.random(), use addition and subtraction to modify the minimum and maximum ranges and then use Math.floor() to chop off the decimal points and make the number a whole number. i.e.

//returns 1 of 10 possible numbers, 0-9
Math.floor(Math.random() * 10);
Rafael Valera
Rafael Valera
8,401 Points
Rafael Valera
Rafael Valera
8,401 Points

Thanks for your reply, Marcus. There is this typecasting feature in Java which I was wondering if JS could support too.. But I'll stick then with floor() function. Greetings

Marcus Parsons
Marcus Parsons
15,719 Points

Cheers, Rafael!