CODEWITHSUNDEEP
functionjavascript
Muhammad Usman
Muhammad Usman

Reputation: 10926

Variable value is not set by JavaScript Function

I have created a variable and tried to set its value by a function. But this value in not accessible outside that function

<script type="text/javascript">
 $(document).ready(function () {
   var pId;
   getProfiles(id,function(b)
     {
        pId=b;
        alert(pId); // It works fine...
      });
  alert(pId); // undefined...
  });
</script>

Upvotes: 2

Views: 2241

Answers (3)

Denis Ermolin
Denis Ermolin

Reputation: 5546

When you assign to pId new value without declaration variable pId declared in global scope. But you have a local pId variable. So when you call alert inside callback it show value of GLOBAL pId and you second alert show your LOCAL pId value.

function f() { d = 2; }; 
function a() {
    var d = 1;
    f();
    alert(d);
}
a();
alert(d);

First alert will show 1 and second will show 2. So second alert in you code will always show undefined no matter when callback called.

Upvotes: 1

mamoo
mamoo

Reputation: 8166

You declare pId but you don't assign any value to it, so by default is undefined, the alert in the same scope is then evaluated, and prints 'undefined'. The anonymous function is a callback that is called by getProfiles() (maybe asynchronously), and you cannot assume that it will be called before the outer alert is called.

<script type="text/javascript">
 $(document).ready(function () {
   /* You declare it but you don't assign any value to it... 
    * so by default is undefined 
    */
   var pId; 
   getProfiles(id,function(b)
     {
        pId=b;
        alert(pId); // This is called only once your anonymous callback is called...
      });
  alert(pId); // Alerts 'undefined'
  });
</script>

Upvotes: 2

Rob Stevenson-Leggett
Rob Stevenson-Leggett

Reputation: 35679

The first alert works because it is just after the value is set by the callback function you're passing to getProfiles.

The second alert in your code example still shows the value "undefined" because the callback function you are passing to getProfiles hasn't executed yet.

Also, just a side note: pId is local to the function you are passing to jQuery's ready event, it is not a global variable.

Upvotes: 3

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