var a = ["a","b","c"]; var b = ["a","b"];  function diff(arr1,arr2){     var newArr = arr1.length>=arr2.length?arr1:arr2.filter(function(ele){      if(arr1.length>=arr2.length?arr2:arr1.indexOf(ele)==-1){           return ele       }     })           return newArr;  }

diff(a,b)

结果是

["a", "b", "c"]

而

a.filter(function(ele){       if(b.indexOf(ele)==-1){           return ele       } })

的结果是
["c"]

在函数中

arr1.length>=arr2.length?arr1:arr2

结果确实是数组a。

arr1.length>=arr2.length?arr2:arr1

也确实是数组b

但运行结果却是不一样。这是为什么？