方法一：

function diff(arr1,arr2){
  var newArr=[];
  for(var i=0;i<arr1.length;i++){
    if(arr2.indexOf(arr1[i])===-1){
      newArr.push(arr1[i]);
    }
  }
  for(i=0;i<arr2.length;i++){
    if(arr1.indexOf(arr2[i])===-1){
      newArr.push(arr2[i]);
    }
  }
  return newArr;
}

方法二：

function diff(arr1, arr2) {
  var newArr = [];
  // Same, same; but different.
  newArr = arr1.filter(function(value){
    return arr2.indexOf(value) < 0;
  });

  
  return newArr.concat(arr2.filter(function(value){
    return arr1.indexOf(value) < 0;
  }));
}


diff([1, 2, 3, 5], [1, 2, 3, 4, 5]);