尝试以下操作：

onClick={() => {
if (count > 0) setCount(count-1)
}}

可以将逻辑分离为单独的函数-第一个函数用于测试计数值，并根据按钮的name在必要时更新状态，第二个函数用于测试状态是否小于/等于零（可用于禁用按钮）。

const { useState } = React;

function Example() {

  const [ count, setCount ] = useState(0);

  // Destructure the name of the button, and
  // increment/decrement the count based on its
  // value. If the count is equal or greater than zero
  // update the state
  function handleClick(e) {
    const { name } = e.target;
    const newCount = name === 'increment'
      ? count + 1
      : count - 1;
    if (newCount >= 0) setCount(newCount);
  }

  // Return true is the state is less than
  // or equal to zero
  function isDisabled() {
    return count <= 0;
  }

  return (
    <div>
      <button
        name="decrement"
        onClick={handleClick}
        disabled={isDisabled()}
      >-
      </button>
      <span className="count">{count}</span>
      <button
        name="increment"
        onClick={handleClick}
      >+
      </button>
    </div>
  );

}

ReactDOM.render(
  <Example />,
  document.getElementById('react')
);

button { width: 25px; height: 25px;}
.count { margin: 0 0.5em; }
button:disabled { background-color: #ffcccc; }

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/17.0.2/umd/react.production.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/17.0.2/umd/react-dom.production.min.js"></script>
<div id="react"></div>