Dereferencing Javascript Variables in Dynamic Methods

Posted April 19, 2006 at 10:46 PM by Ben Nadel

Tags: Javascript / DHTML

There is one problem in Javascript that I cannot seem to get a handle on and it is killling me! I can't seem to get variables to pass by value as I would hope. Take the following example:

for (var intI = 0 ; intI < 10 ; intI++){
var objA = document.createElement( "div" );

// Set the click for the link.
objA.onclick = function(){ alert( intI ); };

// Set the link into the body div.
objDiv.appendChild( objA );
}

Now, in my head, each one of those links, when clicked should alert the appropriate intI value (0, 1, 2, 3, etc.); however, each of them will alert 10 which is the value that broke the FOR loop. It's like they all point to one variable and then get updated for each loop of the FOR iteration.

I can't seem to find a good solution to this. One method that seems to work, but is poop is something along the lines of:

// Define a function INSIDE this function.
function GetI( intX ){
return(
function(){ alert(intX); };
);
}

for (var intI = 0 ; intI < 10 ; intI++){
var objA = document.createElement( "div" );

// Set the click for the link.
objA.onclick = GetI( intX );

// Set the link into the body div.
objDiv.appendChild( objA );
}

This method works as would be expected, though I seem to think that it is doing the exact same thing. It must be something to do with the scoping. Since the intI value is getting passed to a local scope (int GetI()), and then getting passed back, it must be unique (since the local scope of the GetI() method is created unique of each FOR iteration.

This solution seems truly ganky to me. There has to be a better way. And this is just a simple example. I have many places where I want to be doing this with object reference and dynamic event handling. This one simple bumb is really holding me back!




Reader Comments

tc
Aug 20, 2010 at 2:19 PM // reply »
1 Comments

for (var intI = 0 ; intI < 10 ; intI++){
var objA = document.createElement( "div" );
var thisI = intI;

// Set the click for the link.
objA.onclick = function(){ alert( thisI ); };

// Set the link into the body div.
objDiv.appendChild( objA );
}


Aug 20, 2010 at 5:22 PM // reply »
11,244 Comments

@TC,

Won't you still run into the same problem since "thisI" is not re-var'd on each iteration (all var commands are actually run at the top)? Seems like you'd run into the same problem.


Post A Comment

Comment Etiquette: Please do not post spam. Please keep the comments on-topic. Please do not post unrelated questions or large chunks of code. And, above all, please be nice to each other - we're trying to have a good conversation here.

Please review the following issues:

Author Name:


Author Email:

Author Website:

Comment:

Supported HTML tags for formatting: <strong>bold</strong>   <em>italic</em>   <code>code</code>







  • Help Wanted - Find Your Next ColdFusion Job
Ben Nadel's Company - Epicenter Consulting Recent Blog Comments
May 23, 2013 at 11:06 AM
Strange Interaction Between DeserializeJson(), ArrayContains(), And Database Values In ColdFusion
@Ben, Are you talking about As Number: YES As String: YES As Java: YES? If so, that's with 3 different ways of referencing the constant 1, not users.id[1]. Query object references(*) are what seem ... read »
May 23, 2013 at 9:55 AM
Strange Interaction Between DeserializeJson(), ArrayContains(), And Database Values In ColdFusion
@Dan, According to the CF Admin, I'm running Java "1.6.0_45". As far as the DB column, in the database it's an INT. I'll see if I can dig into what CF sees it as. @WebManWalking, But h ... read »
May 23, 2013 at 9:49 AM
Strange Interaction Between DeserializeJson(), ArrayContains(), And Database Values In ColdFusion
@Ben, I think the problem is that we're used to loose typing in ColdFusion, like JavaScript. If a value is a number but it's needed in an expression to be a string, noooo problem. I've encountered ... read »
May 23, 2013 at 9:47 AM
ColdFusion QueryAppend( qOne, qTwo )
You rock! Thank you, thank you, thank you!!! ... read »
May 23, 2013 at 5:19 AM
Ask Ben: Print Part Of A Web Page With jQuery
How to print also the background color of table cells and table lines ... read »
May 23, 2013 at 3:55 AM
Javascript Array Methods: Unshift(), Shift(), Push(), And Pop()
very interesting and helpful too. ... read »
May 22, 2013 at 5:35 PM
Script Tags, jQuery, And Html(), Text() And Contents()
This is still an issue 2 years later. jQuery is supposed to remediate these cross browser issues, no? I have been unable to find any statement from the jQuery team calling this behavior "by de ... read »
May 22, 2013 at 12:44 PM
Ask Ben: Query Loop Inside CFScript Tags
In cf10, if you call a function that has: local.result = {}; local.result.msg = ""; local.svc = new query(); local.svc.setSQL("SELECT * FROM..."); local.obj = local.svc.exe ... read »
InVision App - Prototyping Made Beautiful With Prototyping Tools