js定时器循环展示数组

let currentPage = 0
// arr:原数组 newLen:新数组需要的长度 currentPage:现在的页码

// 方法一：
function loopData(arr, newLen) {
  let len = arr.length;
  let result = len - currentPage;
  let newArr = [];
  if (result > 0 && result < newLen) {
    newArr = [
      ...arr.slice(currentPage - result, len),
      ...arr.slice(0, newLen - result),
    ];
    currentPage = newLen - result;
  } else if (result >= newLen) {
    newArr = arr.slice(currentPage, currentPage + newLen);
    currentPage += newLen;
  } else {
    currentPage = 0;
    newArr = arr.slice(currentPage, currentPage + newLen);
  }
  return newArr;
}

// 方法二：
function loopData(arr, newLen) {
  let len = arr.length;
  let newArr = [];
  if (currentPage === len) {    // 页码等于数组长度时，从0重新开始
    currentPage = 0;
  }
  if (currentPage + newLen <= len) {
    newArr = [...arr.slice(currentPage, currentPage + newLen)];
    currentPage++;
  } else if (currentPage + newLen > len && currentPage < len) {
    newArr = [
      ...arr.slice(currentPage, len),
      ...arr.slice(0, newLen - len + currentPage),
    ];
    currentPage++;
  }
  return newArr;
}

<template>
  <div class="container">
    <el-button @click="changeStatus">{{ flag ? "暂停" : "开始" }}</el-button>
    {{ list }}
  </div>
</template>

<script>
let currentPage = 0;
export default {
  data() {
    return {
      arr: [1, 2, 3, 4, 5, 6, 7],
      list: [],
      timer: null,
      flag: true,
    };
  },
  mounted() {
    this.start()
  },
  destroyed() {
    this.timer && clearInterval(this.timer);
  },
  methods: {
    changeStatus() {
      if (this.flag) {
        this.timer && clearInterval(this.timer);
      } else {
        this.start();
      }
      this.flag = !this.flag;
    },
    start() {
      this.timer = setInterval(() => {
        this.list = this.loopData(this.arr, 4);
      }, 1000);
    },
    loopData(arr, newLen) {
      let len = arr.length;
      let newArr = [];
      if (currentPage === len) {
        currentPage = 0;
      }
      if (currentPage + newLen <= len) {
        newArr = [...arr.slice(currentPage, currentPage + newLen)];
        currentPage++;
      } else if (currentPage + newLen > len && currentPage < len) {
        newArr = [
          ...arr.slice(currentPage, len),
          ...arr.slice(0, newLen - len + currentPage),
        ];
        currentPage++;
      }
      return newArr;
    },
  },
};
</script>

<style lang="scss" scoped>
.container {
  padding: 20px;
}
</style>