前缀表示法字符串计算器Javascript问题

function calculatePrefixExpression(expression) {
  // 解析前缀表示法字符串，将其转换为表达式树
  let tokens = expression.split(' ');
  let stack = [];
  
  for (let i = tokens.length - 1; i >= 0; i--) {
    let token = tokens[i];
    
    if (!isNaN(parseFloat(token))) {
      stack.push(parseFloat(token));
    } else {
      let operand1 = stack.pop();
      let operand2 = stack.pop();
      
      switch (token) {
        case '+':
          stack.push(operand1 + operand2);
          break;
        case '-':
          stack.push(operand1 - operand2);
          break;
        case '*':
          stack.push(operand1 * operand2);
          break;
        case '/':
          stack.push(operand1 / operand2);
          break;
      }
    }
  }
  
  // 返回计算结果
  return stack.pop();
}

// 示例用法
let expression = '+ * 2 3 4';
let result = calculatePrefixExpression(expression);
console.log(result); // 输出：10