全局变量不起作用-largestString() 它将字符串数组作为输入并返回此数组中的最大字符串

Question

 <p id="longeststring">
</p>
  <script>

  var arr=[];
  var longest=arr[0];

  function largestString(arr)
  {
   for (var i=0;i<arr.length;i++)
       {if(arr[i].length>=longest.length)
          {longest=arr[i]}


       }
   return longest;

  }
  z=["what","am","I","doing","now"]
  document.getElementById("longeststring").innerHTML=largestString(z)
</script>

So when var longest=arr[0] is inside the function it works, but when I take it outside, it shows"longest not defined". Why is that? I thought by putting it outside the function, the variable "longest" could update itself.

Thank you in advance.

Answer 1

When you put the expression var longest=arr[0]; outside the function, the arr refers to the global variable. Its value is set to [] , so value of its first item is undefined.

But if you put the expression var longest=arr[0]; inside the scope, the arr refers to the parameter, so it will have the correct value.

Answer 2

@bran0's answer is correct. I suggest you can write var longest = "" instead of var longest = arr[0] because arr 's length may be zero and longest will be undefined in that case.