passing object name as parameter

[cbiti]

Greetings,I'm trying to write a generic isNullEmpty function that takes an object name as a parameter and checks if it exisits and/or if its value is empty. how can I check the existance of an object name when it's passed in as a function parameter? the code below does NOT work. Thanks.

function isNullEmpty(objName)
{
   if (eval(objName))    
   {
      return (eval(objName) == '');  //eval() is not working.
    }
    return true;
} 

[Kravvitz]

It's best to avoid eval(). It's slow and there is usually an alternative.

What exactly are you passing to the function? A string?

[cbiti]

kravvitz, yes, I'm passing the name of the object as a string.

[Pepejeria]

Like Kravvitz said, using eval is in most cases bad practice. Why not just do a null check?

[Kravvitz]

Is the object always global? Or are might you pass something like "object1.object2"?

[cbiti]

well, for now, I'm thinking it might be global, but if we can get it to check on something like object1.object2, that would be sweet.

[kyberfabrikken]

What is the use-case for this? It sounds like you got something completely backwards?

[cbiti]

kyberfabrikken, visual basic has a isNullEmpty property for visual basic strings. my thought is to write this function where I can pass in a string, which can be an object name, or even an element ID and I can check whether that elment exisits document.getElementByID('passedinID') and get it's value to see if it's empty. also I want to use this function to passin global object names and simply check if they exist and/or if their values are empty. I hope this gives you an idea about what I'm trying to do here. Thanks.

[Pepejeria]

Again, just do a null check or check for undefined... Creating a function for this check seems a bit of unnecessary overkill.

[cbiti]

Pepejeria, I guess I see your point in this. but going back to my original question, for a future reference, I would like to know how to execute variable names/object names when they're passed in as a parameter. Thanks.

[kyberfabrikken]

kyberfabrikken, visual basic has a isNullEmpty property for visual basic strings. my thought is to write this function where I can pass in a string, which can be an object name, or even an element ID and I can check whether that elment exisits document.getElementByID('passedinID') and get it's value to see if it's empty. also I want to use this function to passin global object names and simply check if they exist and/or if their values are empty. I hope this gives you an idea about what I'm trying to do here. Thanks.

Not knowing vb, I would guess that isNullEmpty() checks if the value of a variable is null or the variable is undefined. You can implement this by checking if the typeof operator returns "undefined" or the value equals null:

isUndefinedOrNull = function(o) {
  return typeof(o) == 'undefined' || o === null;
}

Combining the function with a check for the existence of an element in the document, would be a bad idea IMHO. Variables in javascript and elements in the DOM are two different things, even if they are tightly integrated. You can create a wrapper function over the horridly longish document.getElementById(), to save the typing though. Most people use $ as the name for such a function - an idea initially coming from the prototype-framework. An implementation could simply be:

$ = function(id) {
  return document.getElementById(id);
}

You can then combine the two functions in one expression, to check if a given element exists in your document:

if (isUndefinedOrNull($("foo"))) {
  alert("no foo");
} else {
  alert("there's a foo, alright");
}