Javascript set variable from within another function?

Question

Say I have a variable called "true" in a function called "test." Then I have another function in a whole different script tag and I want to change "true" using my new function. How can I do this? Thanks.

<script type="text/javascript">
var hello="no";
if(hello=="yes"){ 
  window.onbeforeunload = confirmExit;
  function confirmExit()
  {
    return "Message";
  }
}
</script>

<script type="text/javascript">
function show(id) {
     $('#' + id).show();
     var hello="yes";


}
</script>

It doesnt seem to be working...

It's all about scope. The variable must be defined with var at a higher scope than the functions that use it. Post your code and we can help. Without code, we cannot. — Michael Berkowski
– Michael Berkowski, Commented Sep 24, 2012 at 1:37
Can you create a JSFiddle to demonstrate, true is a reserved word and can't be used for a variable name. It would be nice to see what you're doing. — Pete
– Pete, Commented Sep 24, 2012 at 1:38
var true; function f1() {true = 'hi';} function f2() {true = "something else";} — Michael Berkowski
– Michael Berkowski, Commented Sep 24, 2012 at 1:38
The variable is not actually named true, ill post code one second. — CJ Sculti
– CJ Sculti, Commented Sep 24, 2012 at 1:39

Michael Berkowski · Accepted Answer · 2012-09-24 01:48:43Z

4

In your function, don't use the var keyword. Doing so declares a different variable hello in scope of the function.

// Earlier, you defined the variable at a higher scope here:
var hello="no";
// The function has *not* been called yet, so hello will never equal "yes" when this initially runs.
if(hello=="yes"){ 
  window.onbeforeunload = confirmExit;
  function confirmExit()
  {
    return "Message";
  }
}

function show(id) {
  $('#' + id).show();
  // No var here!
  // the variable was defined at a higher (window) scope already with the var keyword.
  hello="yes";
}

Update:

Your logic is faulty when calling the onbeforeunload. You are never binding the event unless hello == "yes", which it never does when that runs. Instead, check the variable contents in the confirmExit() function:

window.onbeforeunload = confirmExit;
function confirmExit()
{
  if (hello == "yes") {
    return "Message";
  }
}

edited Sep 24, 2012 at 1:48

answered Sep 24, 2012 at 1:41

Michael Berkowski

271k47 gold badges450 silver badges395 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Michael Berkowski Over a year ago

@CJSculti Unless you called the function show(), the variable won't be set at the time it is initially called in the first script block.

CJ Sculti Over a year ago

I do call the function show. I call it onclick of a button. The point is so the box will only work after the button is pressed.

CJ Sculti Over a year ago

And the confirmExit function is called onunload of body, so that should be called last, no?

Rahul · Accepted Answer · 2012-09-24 01:58:43Z

// this will work in your case 
var hello="no";
if(hello=="yes"){
  window.onbeforeunload = confirmExit;
  function confirmExit()
  {
    return "Message";
  }
}
function show(id) {
     $('#' + id).show();
     hello="yes";
}


// Just an small explation of how scope works in Javascript

var hello = "no"; // this has a global scope.
function showGlobal(){
alert(hello); // will alert 'no'
}

function showLocal(){
 var hello ="yes"; // hello is now a local variable. Scope is limited to the function.
 alert(hello); // will alert 'yes'. Scope is local  

}

function showLocalBlock(){

    if(condition == 'true'){
    hello = 'yes';
    }
alert(hello); // will alert yes.

}

// Closure

function ShowClosure(){
 var hello = "yes";
    function ShowInner(){
    alert(hello); // here the variable hello takes the value of the function in which it was defined.

    }  
}

Collectives™ on Stack Overflow

Javascript set variable from within another function?

2 Answers 2

Update:

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Update:

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related