How can I reference an encapsulated javascript function from another encapsulated function?

Question

I'm new to object oriented javascript. I have a set up method that I want to a) check if an element is null and if so wait and call itself again and b) observe the click event of a button.

ErrorBox.prototype.setUpErrorBox = function(btnClientID) {
    if (btnClientID == null) {
        setTimeout("setUpErrorBox()", 1000)
        return;
    }
    Event.observe(btnClientID, 'click', setValSummary);
}

I'm getting errors that setUpErrorBox and setValSummary don't exist (which they don't). How can I reference them? I tried this.setValSummary which didn't work.

In other words, how do I call the equivalent of a class's method from another method of the same class in javascript?

You want it to call itself every second? (since the call you setup with setTimeout has no arguments, and undefined == null, it will keep calling itself with the timeout) — some
– some, Commented Feb 18, 2009 at 20:58
in theory, yes it would call itself every second. in reality, i want to make sure that asp .net has completely loaded the page before i try to observe the click event. — rmw
– rmw, Commented Feb 18, 2009 at 21:26
But the code make no sense: If it's called without a parameter, or a parameter that has the primitive value of 'undefined' or 'null', it will keep calling itself until the end of the world: Since the call in the setTimeout has no parameter, the if-statement will NEVER be false. It makes no sense! — some
– some, Commented Feb 19, 2009 at 4:46
the purpose of the timeout is not to check if it was called without a parameter, it's to check that the button element has loaded and exists on the page. yes, this code would bomb if called without a parameter but it's not a multi-purpose API. — rmw
– rmw, Commented Feb 19, 2009 at 16:40

Community · Accepted Answer · 2017-05-23 12:19:01Z

2

Use closures to hold on to your execution context:

ErrorBox.prototype.setUpErrorBox = function(btnClientID) 
{
   var box = this; // object context reference
   if (btnClientID == null) 
   {
      // use closure as event handler to maintain context
      setTimeout(function() { box.setUpErrorBox() }, 1000)
      return;
   }
   // again, use closure as event handler to maintain context
   Event.observe(btnClientID, 'click', function() { box.setValSummary() });
}

1 Comment

some Over a year ago

'self' is already defined in the global scope. Using it as a name for a local variable is not recommended.

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See also: JavaScript Callback Scope

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