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JavaScript

Posted by Ned Redmond
Ned Redmond
5,615 Points

Using a dropdown in Javascript: why won't it work?

https://codepen.io/nred/pen/oyBGxN

I am trying to build a dice roller inspired by the Object Oriented Javascript "Dice Roller 2015" project.

However, I can't figure out how to get the dropdown value (to choose dice sides) to feed into the dice roll function.

No matter what I try, whenever I trigger the dice roll, I get a d4 roll. What is happening here?

Relevant bits:

HTML:

<select id="typeDie" onchange="getDieType()">
    <option value="4">d4</option>
    <option value="6">d6</option>
    <option value="8">d8</option>
    <option value="10">d10</option>
    <option value="12">d12</option>
    <option value="20">d20</option>
    <option value="100">d100</option>
</select>

Javascript:

//gets sides from dropdown in ui
function getDieType() {
    return parseInt(document.getElementById("typeDie").value);
}

//determines number of sides
function Dice(sides) {
  this.sides = sides;
}
let dieRoll = new Dice(getDieType());

//generates roll based on number of sides
Dice.prototype.roll = function () {
  return Math.floor(Math.random() * this.sides) + 1;
}

1 Answer

James Anwyl
.a{fill-rule:evenodd;}techdegree seal-36
James Anwyl
Full Stack JavaScript Techdegree Graduate 49,960 Points

Hi Ned,

When your app loads, a new object is created using the Dice constructor function. It gets stored in the variable dieRoll.

let dieRoll = new Dice(getDieType());

When you click the button, the value stored in dieRoll doesn't change. So the number of sides is always 4.

Try moving the dieRoll = new Dice(getDieType()) into your button.onclick function 

button.onclick = function() {

  let dieRoll = new Dice(getDieType());

  let result = dieRoll.roll();

  console.log("result:", result);
};

This way, each time the button is clicked, the Dice constructor gets called and a new object is created (using the value of #typeDie).

A more concise way:

button.onclick = function() {
  var result = new Dice(getDieType()).roll();
  console.log(result);
};

Hope this helps :)

Ned Redmond
Ned Redmond
5,615 Points

Thank you! That works!