无法使闪光灯连续闪烁并在点击按钮时停止

<button id="stopButton">停止闪烁</button>
<div id="flashlight"></div>

#flashlight {
  width: 100px;
  height: 100px;
  background-color: yellow;
  animation: blink 1s infinite;
}

@keyframes blink {
  0% {
    background-color: yellow;
  }
  50% {
    background-color: black;
  }
  100% {
    background-color: yellow;
  }
}

var intervalId;

function startBlink() {
  var flashlight = document.getElementById("flashlight");
  intervalId = setInterval(function() {
    flashlight.style.backgroundColor = flashlight.style.backgroundColor === "yellow" ? "black" : "yellow";
  }, 500);
}

function stopBlink() {
  clearInterval(intervalId);
}

document.getElementById("stopButton").addEventListener("click", stopBlink);

startBlink();