es6中selectedSubreddit(,a1)怎么传递参数为什么错误？

Question

function selectedSubreddit(state = 'reactjs', action) {
    switch (action.type) {
      case 'tr':
        return '突然'
        default:
            return state
    }
}

var a1 = {
  type: 'tr'
}

let selected = selectedSubreddit(,a1);
console.log(selected);

function selectedSubreddit(action,state = 'reactjs') {
    switch (action.type) {
      case 'tr':
        return '突然'
        default:
            return state
    }
}

var a1 = {
  type: 'tr'
}

let selected = selectedSubreddit(a1, );
console.log(selected); // 突然

Answer 1

• 问题中的示例，有默认值的参数state并不是尾参数，所以无法只省略这个参数，解决方法可以调用时显示输入undefined，即let selected = selectedSubreddit(undefined, a1);
• 或者function selectedSubreddit(action, state = 'reactjs') { }，然后调用let selected = selectedSubreddit(a1, );