Javascript/jQuery I can't stop time with setTimeout, error find variable

Question

I use setTimeout to create a time countdown of 5 seconds (it works), but I want to stop the setTimeout with Button Stop, but I have an error finding the variable.

What is the error?

function newTime(ob) {
    
    if(ob==undefined){
        const myTimeout = setTimeout(myGreeting, 5000);
        console.log("Start>");
    }
    if(ob=="stop"){
        if(myTimeout==true){
            clearTimeout(myTimeout);
            console.log("Stop>");
        }
    }
    
}

function myGreeting() {
  document.getElementById("demo").innerHTML = "Happy Birthday!"
}

function myStopFunction() {
  newTime("stop");
}

<h1>The Window Object</h1>
<h2>The setTimeout() and clearTimeout() Methods</h2>

<p>Click "Stop" to prevent myGreeting() to execute. (You have 5 seconds)</p>

<button onclick="myStopFunction()">Stop!</button>
<button onclick="newTime()">new Time Start</button>

<h2 id="demo"></h2>

Answer 1

That's because const and let variables are block-scoped. In your case, you declared myTimeout inside the if block, so the myTimeout variable will only be available inside that if block.

To illustrate this better:

1) This will give you a variable not defined error

if (true) {
    let foo = 'ok'; 
}
console.log(foo);

2) This won't:

let foo;
if (true) {
    foo = 'ok'; 
}
console.log(foo);

Also, you'll have to declare your variable outside your function, otherwise you won't have access to the value assigned to it on the previous call.