实现数组扁平化的三种方法``` ``` function flatten(arr) { return arr.reduc

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    <title>Document</title>
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    <script>
      const arr = [1, 2, 3, [4, 5, [6, 7, 8]]];

      // 1.es6 flat
      console.log(arr.flat(Infinity)); //[1, 2, 3, 4, 5, 6, 7, 8]

      //2.
      let res = JSON.stringify(arr).replace(/\[|\]/g, "");
      console.log(res); //1,2,3,4,5,6,7,8
      res = JSON.parse("[" + res + "]");

      console.log(res);

      //3.reduce 方法：
      function flatten(arr) {
        return arr.reduce((result, item) => {
          return result.concat(Array.isArray(item) ? flatten(item) : item);
        }, []);
      }
      console.log("reduce", flatten(arr));
    </script>
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