javascript - Math.Random to draw image -

i trying use math.random draw image.

though know haven't got right.

i know need loop go through math.random function, don't know how implement it. know spawnrock function isn't correct not know how fix it. help?

this code breaks current drawimages.

        var num;          function mathrock() {             var x = math.floor((math.random() * 10) + 1);             document.getelementbyid("num").innerhtml = x;             }          function spawnrock() {         if (num = 2, 4, 8){              context.drawimage(rock, 1500, 450);             } else {                 }          var rock = new image();         rock.src = "rock.png"; 

here's quick primer on math.random

math.random() * x generate random floating point number between 0 (but not including) x. math.random*10 generate, example, 0.22, 1.56, 7.92 9.9999999999.

if need random integers, can strip off non-integer portion of random number parseint( math.random()*10 ) generate 0,1,2,3,4,5,6,7,8,9.

if want random "coin-flip" (true or false) can this:

var randomtruefalse=(math.floor(math.random()*2)==0); 

if need do randomly 3 out of 10 times can this:

var thirtypercentsuccess=( (math.random()*10-7)>=0 ); 

then use desired version of random number choose whether draw or else:

if (thirtypercentsuccess){      context.drawimage(rock, 1500, 450); }else{     // else }