How to make a variable not used out of scope?

Question

How can I make this variable not used out of scope. I keep getting this error in JSFiddle: 'variable' Used out of scope. I don't know what that means or why it occurs. I tried to fix it myself and that just made it worse. I looked all over the internet and couldn't find anything, so stack overflow was my last resort. Anyways, here is my code. Or, If you don't prefer JSFiddle, here:

var dollar = 0;
var cents = 0;

function plusOne() {
  if (cents < 95) {
    var cents = cents + 5;
    document.getElementById("amount").innerHTML = cents + " ¢";
  } else if (cents == 95) {
    var dollar = 1;
    document.getElementById("amount").innerHTML = dollar + " $";
  } else if (cents == 100) {
    var cents = 0;
    var dollar = dollar + 0.05;
    document.getElementById("amount").innerHTML = dollar + " $";
  }
}

<button onclick="plusOne()">Plus five cents</button>
<p id="amount">0 ¢</p>

As you can see, it does not change the value at all. I don't know what is going on with it.

Answer 1

You can't over declare the var's

var dollar = 0;
var cents = 0;

function plusOne() {
  if (cents < 95) {
    cents = cents + 5;
    document.getElementById("amount").innerHTML = cents + " ¢";
  } else if (cents == 95) {
    dollar = 1;
    document.getElementById("amount").innerHTML = dollar + " $";
  } else if (cents == 100) {
    cents = 0;
    dollar = dollar + 0.05;
    document.getElementById("amount").innerHTML = dollar + " $";
  }
}

<button onclick="plusOne()">Plus five cents</button>
<p id="amount">0 ¢</p>

Answer 2

At the beginning try don't declare variables using var. Use 'const' when you know value and this value is constans otherwise use 'let'.

let dollar = 0;
let cents = 0;

function plusOne() {
  if (cents < 95) {
    cents += 5;
    document.getElementById("amount").innerHTML = cents + " ¢";
  } else if (cents == 95) {
    dollar = 1;
    document.getElementById("amount").innerHTML = dollar + " $";
  } else if (cents == 100) {
    cents = 0;
    dollar =+ 0.05;
    document.getElementById("amount").innerHTML = dollar + " $";
  }
}