javascript - How do I set up "var count" so that it is initialized the first time and then incremented? - Stac

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I tried this:

var count;

function testCount ()
{
  if (count)
  {
    alert("count is: " + count);
    count++;
  }    
  else
  {    
    alert("count is: " + count);
    var count = 0;
  }
};

testCount();

but it always gives "undefined" and the value of count is not updated when I run it again in jsfiddle.

I tried this:

var count;

function testCount ()
{
  if (count)
  {
    alert("count is: " + count);
    count++;
  }    
  else
  {    
    alert("count is: " + count);
    var count = 0;
  }
};

testCount();

but it always gives "undefined" and the value of count is not updated when I run it again in jsfiddle.

• javascript

Share Improve this question Follow asked Nov 12, 2011 at 18:38 ZeynelZeynel 13.5k3131 gold badges103103 silver badges148148 bronze badges

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4 Answers 4

Sorted by: Reset to default 2

Just initialize it at declaration:

var count = 0;

And don't declare a second count within your else. That's a pletely separate variable.

The problem in your code is that the count within the else block is different from the one you have declared in the global scope. This happens because you are defining a new variable with the same name by using var count = 0; within the else clause which will not be referring to the count variable declared outside of the function.

If you remove the var withing your else, things will work as you expect:

var count;

function testCount ()
{
  if (count)
  {
    alert("count is: " + count);
    count++;
  }    
  else
  {    
    alert("count is: " + count);
    count = 0;
  }
};

testCount();

However, if you call testCount again, the if will evaluate to false, as 0 is a "falsey" value in Javascript.

It appears that nobody has shown the simple testCount() implementation. Just initialize it upon declaration and then just use it in your function:

var count = 0;

function testCount ()
{
    alert("count is: " + count);
    count++;
}

testCount();

Assuming you cant just

var count = 0;

You can detect its lack of an assigned value with;

if (typeof count === 'undefined')
   count = 0;

It is a problem of variable scope.

When outside a function, you define a variable, this variable is global. In other word, when you do :

var count;

You declare count, and you can use it everywhere.

Now, in a function, when you declare count as below :

function testCount ()
{
    ...
    alert("count is: " + count);
    var count = 0;
    ...
};

you declare a new variable whose scope is in the function, and initialize it with 0. However, what you want is to change the global variable value. So, just do that :

function testCount ()
{
    ...
    alert("count is: " + count);
    count = 0;
    ...
};

Note that I have removed the var keyword.

Now, to simplify the whole program, I suggest you that :

var count = 0;

function testCount ()
{
    alert("count is: " + count);
    count++;
};

• the initialization is made with the declaration
• so you do not need to worry about the initialization inside testCount
• your code is lighter

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