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JavaScript JavaScript Loops, Arrays and Objects Simplify Repetitive Tasks with Loops For Loops

Mark Libario
Mark Libario
9,003 Points
Posted by Mark Libario
Mark Libario
9,003 Points

How can I print different numbers per DIV?

Guys need help!

Im already in the objects course but Im going back to review and apply these stuff.

What I wanted to do is to imitate a lottery draw.

I created an object that holds a lottery number and holds a function that draws that number randomly from 1 - 49.

I wanted the page to print out my 6 divs that contains 6 different numbers from the lottery object.

However, idk how to do it. I just end up printing 6 numbers and all the same numbers..

can anyone show me how to do it right?

Im thinking of an array or something like adding a new property on the object for each draw and then prints out all the numbers in the array or in the object, something like this.

Here is my JavaScript:

function lotto (number) {
  this.number = number;
  this.drawNumber = function () {
    return Math.floor(Math.random() * number) +1;
  }

}

var lottoNumber = new lotto (49);
var draw = lottoNumber.drawNumber ();
let html = "";


for (let i = 0 ; i < 6; i+= 1) {
  html += "<div>" + draw + "</div>";
}
document.write (html);

2 Answers

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

You're getting the same number because you only pick a random number once before the loop, and then just print the same number over and over in the loop. You can change this by picking the random number inside the loop:

  html += "<div>" + lottoNumber.drawNumber() + "</div>";

But even this might not be what you really want, since sometimes you will get the same number chosen randomly more than once but lotto numbers must all be unique. To accomplish this, you might want to pick the numbers much like they do in real life using the ping-pong balls. Your "balls" could be an array with all the numbers, and for each pick you could select one at random and then remove it from the array. So every choice would be made from a slightly smaller set.

Also, by convention constructor function names start with a capital letter.

Mark Libario
Mark Libario
9,003 Points
Mark Libario
Mark Libario
9,003 Points

but by doing lottoNumber.drawNumber () , isnt it the same thing as I did because i placed that function in the variable named draw. so instead of typing the whole thing, al i need to do is typed draw that calls that function.. I dont get it :/

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

What the original code does is invoke (same thing as "call") the function, and put the result (the random number it picked) in the variable named "draw". So "draw" represents the number, not the function itself.

Mark Libario
Mark Libario
9,003 Points
Mark Libario
Mark Libario
9,003 Points

Oh i see, that's true! I totally forgot about that. it's like naming a variable, and then using prompt. Thanks!

I tried to put the same like you mentioned, however it gives me this:

function () { return Math.floor(Math.random() * number) +1; }function () { return Math.floor(Math.random() * number) +1; }function () { return Math.floor(Math.random() * number) +1; }function () { return Math.floor(Math.random() * number) +1; }function () { return Math.floor(Math.random() * number) +1; }function () { return Math.floor(Math.random() * number) +1; }

its like repetitive of what is inside of the this,drawNumber and not giving a number instead.

Im using this Workspace for reference: https://teamtreehouse.com/library/for-loops-2

I am just working on the javascript side.

Mark Libario
Mark Libario
9,003 Points
Mark Libario
Mark Libario
9,003 Points

I got it now! 

function Lotto (number) {
  Lotto.number = number;
  Lotto.drawNumber = Math.floor(Math.random() * number) +1;


}


let html = "";


for (let i = 0 ; i < 6; i+= 1) {
  Lotto(49);
  html += "<div>" + Lotto.drawNumber + "</div>";
}
document.write (html);

I did something like this.

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

Sure, that would work, but it's a bit unusual:

  • "Lotto" is no longer a constructor but the convention for normal function names is lower case
  • functions don't normally have value properties attached to them

You might do the same thing a bit more conventionally (and compactly) like this:

function lottoPick(number) {
  return Math.floor(Math.random() * number) + 1;
}

let html = "";
for (let i = 0; i < 6; i += 1) {
  html += "<div>" + lottoPick(49) + "</div>";
}
document.write(html);
Marco Poletto
PLUS
Marco Poletto
Courses Plus Student 10,099 Points
Marco Poletto
Marco Poletto
Courses Plus Student 10,099 Points

You should run the random number generator inside the for loop. Something like that

for (let i = 0 ; i < 6; i+= 1) { 
   let numberLoop = lotto(49); 
   html += "<div>" + numberLoop + "</div>"; 
}

I haven't tested it but it should work

Steven Parker
Steven Parker
231,275 Points
Steven Parker
Steven Parker
231,275 Points

Note that "lotto" is a constructor function and doesn't return anything.