I have a question relative to this code. It should (and it does) display a list of items, where you can add and remove entries by clicking on the plus and minus.
<html><head><script src="http://www.google.com/jsapi"></script>
<script>
google.load("jquery", "1.3.2");
app={};
app.attachList = function() {
return {
_current_id : 0,
addFilterAfter : function(after_entry_id) {
that = this;
new_id = this._newId();
jQuery("#entry_"+after_entry_id).after("<li id=\"entry_"
+new_id+"\"><a href=\"javascript:void(0);\" id=\"entry_"
+new_id+"_add\">(+)</a><a href=\"javascript:void(0);\">(-)</a> hello "
+new_id+"</li>");
jQuery("#entry_"+new_id+"_add")
.bind("click", function() {
that.addFilterAfter(new_id);
}
);
},
show : function() {
that = this;
new_id = this._newId();
jQuery("#list").children().remove();
jQuery("#list").append("<li id=\"entry_"
+new_id+"\"><a href=\"javascript:void(0);\" id=\"entry_"
+new_id+"_add\">(+)</a> hello </li>");
jQuery("#entry_"+new_id+"_add")
.bind("click", function() {
alert(new_id); // HERE
that.addFilterAfter(new_id);
}
);
},
_newId : function() {
this._current_id++;
return this._current_id;
},
};
}
app.main = function() { l = app.attachList(); l.show(); }
google.setOnLoadCallback(function() { jQuery.noConflict(); jQuery(document).ready(app.main); });
</script>
<ul id="list" /></ul>
</head>
</html>
My question is relative to what happens at the line marked HERE. Ideally, if I click the first item +, I would expect this code to continue adding just below the first item. This does not happen. It continues incrementing the new_id (as you can see from the alert) instead of keeping the original new_id it was granted.
Now, I have a suspect about what's going on, mostly involving the closure nature of javascript, but I want to hear it explained from someone more skilled.
As a side note, if I partition the logic for binding the event in a separate method, it works as expected... from this my suspect.
1 Answer 1
The problem that is causing this behavior in your code is that you're missing the var statement when you assign a value to new_id.
In JavaScript when you make an assignment to an undeclared identifier (an identifier not reachable in the scope chain), it becomes global (window.new_id is created) and that's why it keeps incrementing.
2 Comments
var anymore in my javascript life.