When the start button is clicked once, everything works perfectly fine. However, when the start button is clicked multiple times (by accident for example), the speed of the counter increases and the stop button doesn't seem to work any more!
Why is this happening? And what can I do to prevent the start button (if clicked accidentally) from increasing the speed of the timer when it is already running?
<button id="startBtn" onclick="startTimer()">Start</button>
<button id="stopBtn" onclick="stopTimer()">Stop</button>
<h2 id="timer"></h2>
<script>
let myCounter
function startTimer() {
myCounter = setInterval(counter, 200);
}
function stopTimer() {
clearInterval(myCounter);
}
let i = 0;
function counter() {
document.getElementById("timer").innerHTML = i++;
}
</script>Welcome to StackOverflow.
Within your question, it's unclear if you want the timer to reset if the user clicks the start button again, however with my answer, I came to the conclusion that you didn't.
Here's a modified version of startTimer() which utilizes a guard clause to check if an interval already exists (and if so, don't start again)
function startTimer() {
// Guard clause! If the counter exists, exit the function!
if(myCounter) {
return
}
myCounter = setInterval(counter, 200);
}
A tiny update of the stop function is also needed to set myCounter to null after the counter is stopped:
function stopTimer() {
clearInterval(myCounter);
// Set the counter to Null, because it is still declared even though it has no value! (try removing this line and see what happens when you hit start again)
myCounter = null;
}
Hope this helped :)
I added a variable that can helps you detect if the counter is already clicked or not, with the condition of that variable, you can have what you want, I edited your code.
<button id="startBtn" onclick="startTimer()">Start</button>
<button id="stopBtn" onclick="stopTimer()">Stop</button>
<h2 id="timer"></h2>
<script>
let myCounter
let clicked = false;
function startTimer() {
if(!clicked){
myCounter = setInterval(counter, 200);
}
clicked = true;
}
function stopTimer() {
if(clicked){
clearInterval(myCounter);
}
clicked = false;
}
let i = 0;
function counter() {
document.getElementById("timer").innerHTML = i++;
}
</script>You could simply disable the start button once clicked, and re-enable it when the stop button is clicked.
let i = 0;
let myCounter;
let startBtn = document.getElementById('startBtn');
let stopBtn = document.getElementById('stopBtn');
let timer = document.getElementById('timer');
function startTimer() {
startBtn.disabled = true;
stopBtn.disabled = false;
myCounter = setInterval(counter, 200);
}
function stopTimer() {
startBtn.disabled = false;
stopBtn.disabled = true;
clearInterval(myCounter);
}
function counter() {
i++; timer.value = i;
}
startBtn.addEventListener('click', startTimer);
stopBtn.addEventListener('click', stopTimer);<button id="startBtn">Start</button>
<button id="stopBtn" disabled>Stop</button>
<h2><output id="timer">0</output></h2>As an added measure, you can even hide the disabled button so only the active one is shown.
button:disabled {
display: none;
}