variable in object string

[bmgz]

sorry for the stupid question, bu6 I haven't been able to find the
answer anywhere..

consider this useless function which assigns an object to a var..

function(myPara m){
var select1 = document.myForm .mySelectName;
}

I simply want this line to subsitute "mySelectNa me" with a var string

function(myPara m){
var select1 = document.myForm .myParam;
}

It doesn't work, ive tried umpteen variations with []+ "" '' etc..
How would I do this stupid-simple thing?

[Martin Honnen]

bmgz wrote:

function(myPara m){
var select1 = document.myForm .myParam;

var select1 = document.myForm .elements[myParam];

but in most cases you can simply pass around objects like for instance
the form or select itself, there is hardly the need to pass in a string
to use it to find an object reference.

--

Martin Honnen
http://JavaScript.FAQTs.com/

[VK]

Each object inherits hash (associative array) mechanics, this is how
objects properties are stored. So:

function f1(propertyName ) {
var myVar = someObject[propertyName];
// in the particular:
// var myVar = document.formNa me[propertyName];
}

[Mick White]

bmgz wrote:
[...]

function(myPara m){
var select1 = document.myForm .myParam;
}

It doesn't work, ive tried umpteen variations with []+ "" '' etc..
How would I do this stupid-simple thing?

Are you passing an object or a string?

Mick

[bmgz]

Mick White wrote:

bmgz wrote:
[...]

function(myPara m){
var select1 = document.myForm .myParam;
}

It doesn't work, ive tried umpteen variations with []+ "" '' etc..
How would I do this stupid-simple thing?

Are you passing an object or a string?

Mick

An object, I want to know how to refer to the object that triggered the
function?

[bmgz]

bmgz wrote:

Mick White wrote:

bmgz wrote:
[...]

function(myPara m){
var select1 = document.myForm .myParam;
}

It doesn't work, ive tried umpteen variations with []+ "" '' etc..
How would I do this stupid-simple thing?

Are you passing an object or a string?

Mick

An object, I want to know how to refer to the object that triggered the
function?

oh um, from within the function itself..
ie.

function(){
var a = "[the object that called me ie. myButton]";
}

<input type="button" name="mybutton" onclick='functi on();' />

[RobG]

bmgz wrote:
[...]

An object, I want to know how to refer to the object that triggered
the function?

oh um, from within the function itself..
ie.

function(){
var a = "[the object that called me ie. myButton]";
}

<input type="button" name="mybutton" onclick='functi on();' />

You have to pass a reference in your onclick:

<input type="button" name="mybutton" onclick="functi on(this);" />

in the script of your onclick use 'this' ---------------^^^^
Then in your function:

function( a ){
alert( 'the object that called me is ' + a );
...
}

or

function(){
alert( 'the object that called me is ' + arguments[0] );
...
}

--
Rob

[VK]

> want to know how to refer to the object that triggered the function?

from within the function itself..

Oh I see now... It depends on how your function was called: by event
capturer or by another function during normal program flow.

If by event capturer, then you simply *cannot* do it.
At least nothing reliable that would work for all browsers. You can do:

function myFunction(e) {
// "e" argument is important placeholder
// in case of working in NN/DOM event model
// IE sets global "event" variable for you
var myCaller = (e)? e.currentTarget : event.srcElemen t;
}

Of course you have to add event capturers programmically in this case.
You cannot do <element onclick="myFunc tion()">,
Empty parenthesis will kill the "e" and the script will fail for FF &
Co
You have to:
obj.onclick = myFunction;
or
using addEventListene r (DOM) / attachEvent (IE) methods

This works fine as long as there is no more elements below the element
that capturing events. Otherwise all this mess fails onto the ground.
In FF you still can get the right object by using currentTarget. But in
IE event.srcElemen t will point to the first element in the bubble
history. So in the majority of situations your only option is to use
intrinsic capturers and "manually" forward the right object to the
function: <element onclick="myFunc tion(this)">

If your function is called by another function during normal program
flow, you can check the caller property.
function myFunction {
if (myFunction.cal ler != null) {
myCaller = myFunction.call er
}
else {
// I'm the first one!
}
}

P.S. There is a lot of bubbles in docs about "caller is deprecated".
But deprecation doesn't mean "removal", it means "substituti on". As
long as *no one* provided a reasonable substitution for caller, we just
keep using it. It's supported by all main browsers.

[Michael Winter]

On 19/06/2005 12:58, VK wrote:

want to know how to refer to the object that triggered the function?
from within the function itself..

[snip]
If by event capturer, then you simply *cannot* do it.
Of course you can.

<... onclick="myFunc tion(this);">

function myFunction(elem ent) {
/* The element argument is a reference to the HTML element */
}

Or:

<... id="myElement" >

document.getEle mentById('myEle ment').addEvent Listener(
'click',
function() {
/* The this operator refers to the HTML element, myElement */
},
false
);

Or:

<... id="myElement" >

document.getEle mentById('myEle ment').onclick = function() {
/* The this operator refers to the HTML element, myElement */
};
function myFunction(e) {
[...]
var myCaller = (e)? e.currentTarget : event.srcElemen t;
}
You've been told before that referring directly to the event identifier
is not wise as it could be undefined in some browsers. Refer to it via
the global object and test that it exists.

Also, the above could produce very wrong results: the currentTarget and
srcElement properties refer to very different things. The former is the
same as the element variable or the this operator in my examples, whilst
the latter (and the target property) refer to the original element that
fired the event.
Of course you have to add event capturers programmically in this case.
You cannot do <element onclick="myFunc tion()">,
Empty parenthesis will kill the "e"
So instead, one could write:

<... onclick="myFunc tion(event);">

or to be really cautious:

<... onclick="myFunc tion(('object' == typeof event) && event);">

The first argument to myFunction will either be false or an event object.

[snip]
P.S. There is a lot of bubbles in docs about "caller is deprecated".
But deprecation doesn't mean "removal", it means "substituti on".
Deprecation often means this feature may be removed in the future, and
more generally, this feature should not be used.

As far as ECMAScript is concerned, the caller property has never
existed, which is potentially a bigger concern than whether or not it is
deprecated.

Finally, the caller property doesn't provide the information that the OP
wants, at least as I understand the problem.
As long as *no one* provided a reasonable substitution for caller, we just
keep using it.

If a function must really need to know what called it, then it should
have a required argument that contains a reference to the relevant
function object. No-one needs to provide a substitute for the caller
property as it isn't necessary.

Mike

--
Michael Winter
Replace ".invalid" with ".uk" to reply by e-mail.

[VK]

>> from within the function itself.

That was the keyword in OP. The "manual feeding" of the right object
was already given by RobG.
But what if we need to keep our HTML/XML code and scripting totally
separate?
The code below illustrates the problem many posters in this group
really encounting (even w/o knowing it):

<html>
<head>
<title>Event target</title>
<meta http-equiv="Content-Type" content="text/html;
charset=iso-8859-1">
<script type="text/javascript">
function init() {
document.getEle mentById('DIV1' ).onclick = f1;
}

function f1(e) {
var myTarget = ((e)&&(e.curren tTarget))?
e.currentTarget : event.srcElemen t
alert(myTarget. id);
}

window.onload = init;
</script>
</head>

<body>
<div id="DIV1">DIV 1
<span id="SPAN1">SPA N 1</span>
</div>
</body>
</html>

Click on "SPAN 1" (nested element). FF still works properly grace to
the e.currentTarget property. This is actually why you should not use
e.target unless you're making some event tracking.
e.target will fail in any more or less complicated situation.

event.srcElemen t shows as before the original event source (SPAN1).
There is *no* way to tell from the function itself that the actual
event capturer is DIV1. The only side walk is using closures with
memory leak in IE.

You find a way (w/o closures, w/o inline "helpers") - you'll be better
than the whole Microsoft. ;-)