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

Adriano Provenzano
Adriano Provenzano
2,144 Points
Posted by Adriano Provenzano
Adriano Provenzano
2,144 Points

Random number in js

why is my browser showing me the random number as undefined?

3 Answers

Steven Parker
Steven Parker
229,732 Points
Steven Parker
Steven Parker
229,732 Points

Are you typing this into the console?

Math.random()

If you're doing something else, show your exact code here for analysis.

And if you are typing exactly that into the console and getting "undefined" — I recommend you try a different browser!

Adriano Provenzano
Adriano Provenzano
2,144 Points
Adriano Provenzano
Adriano Provenzano
2,144 Points

var question= prompt("What's your favorite number?"); var number = parseInt(question); var sentence = "Your favorite number: " + number; sentence += " means....." + random; var random = Math.floor(Math.random()*2)+1;

document.write(sentence);

It is a stupid example but it should work...

Steven Parker
Steven Parker
229,732 Points
Steven Parker
Steven Parker
229,732 Points

Oh, that's just a matter of the order of execution. You referenced "random" on the line before it was assigned, so at that moment its value is literally "unassigned".

Just swap the order of that line and the one that assigns it and you'll get a numeric result (either 1 or 2 based on that formula).

Joseph Wasden
Joseph Wasden
20,406 Points
Joseph Wasden
Joseph Wasden
20,406 Points

Are you assigning a variable a value? If you assign a variable a value, it will return the current value of the variable before performing the assignment. So, it will seem as if it has assigned it undefined. However, it will have completed the assignment after having returned the current value. See the image below.

https://imgur.com/peEvBSr

Joseph Wasden
Joseph Wasden
20,406 Points
Joseph Wasden
Joseph Wasden
20,406 Points

You aren't assigning random before trying to use it to assign to sentence.

        var question = prompt("What's your favorite number?"); 
        var number = parseInt(question); 
        var random = Math.floor(Math.random()*2)+1; // moved up in code to resolve assignment before use in sentence assignment.
        var sentence = "Your favorite number: " + number; sentence += " means....." + random; // now we can get a value for random other than undefined, since we defined it.

        document.write(sentence);