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<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JS Bin</title>
</head>
<body>

<script id="jsbin-javascript">
var test = [1,2,33,[55,88,[23,[211],66,998],2000],4,2002,[111,58,22,[120],15],68];

function nestedArray(oldArr, newArr) {
  newArr = newArr || []
  oldArr.forEach(function(item,index){
    if(Array.isArray(item)){
      return nestedArray(item, newArr);
    }else{
      newArr.push(item)
    }
  })
  return newArr
}

console.log(nestedArray(test))
</script>


<script id="jsbin-source-javascript" type="text/javascript">var test = [1,2,33,[55,88,[23,[211],66,998],2000],4,2002,[111,58,22,[120],15],68];

function nestedArray(oldArr, newArr) {
  newArr = newArr || []
  oldArr.forEach(function(item,index){
    if(Array.isArray(item)){
      return nestedArray(item, newArr);
    }else{
      newArr.push(item)
    }
  })
  return newArr
}

console.log(nestedArray(test))</script></body>
</html>